diff --git a/applications/test/parallel-waitSome/Make/files b/applications/test/parallel-waitSome/Make/files
new file mode 100644
index 0000000000..b27e308ef6
--- /dev/null
+++ b/applications/test/parallel-waitSome/Make/files
@@ -0,0 +1,3 @@
+Test-parallel-waitSome.C
+
+EXE = $(FOAM_USER_APPBIN)/Test-parallel-waitSome
diff --git a/applications/test/parallel-waitSome/Make/options b/applications/test/parallel-waitSome/Make/options
new file mode 100644
index 0000000000..18e6fe47af
--- /dev/null
+++ b/applications/test/parallel-waitSome/Make/options
@@ -0,0 +1,2 @@
+/* EXE_INC = */
+/* EXE_LIBS = */
diff --git a/applications/test/parallel-waitSome/Test-parallel-waitSome.C b/applications/test/parallel-waitSome/Test-parallel-waitSome.C
new file mode 100644
index 0000000000..b17bb6e345
--- /dev/null
+++ b/applications/test/parallel-waitSome/Test-parallel-waitSome.C
@@ -0,0 +1,328 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2023 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Application
+    Test-parallel-waitSome
+
+Description
+    Test polling versus wait-all for processing receive data.
+    Will not see much difference between -wait-all and -no-polling though
+    since the master doesn't have enough other work.
+
+\*---------------------------------------------------------------------------*/
+
+#include "List.H"
+#include "argList.H"
+#include "Time.H"
+#include "IPstream.H"
+#include "OPstream.H"
+#include "IOstreams.H"
+#include "Switch.H"
+#include "clockTime.H"
+
+using namespace Foam;
+
+
+// The 'classic' waiting receive, but also only waiting for recv request
+template<class Type>
+void waitingReceive
+(
+    const labelRange& recvRequests,
+    const List<List<Type>>& recvBuffers,
+    const bool waitAll = false
+)
+{
+    clockTime waitTiming;
+
+    if (waitAll)
+    {
+        // Wait for send and recv (assumes recv followed by send)
+        UPstream::waitRequests(recvRequests.start(), -1);
+    }
+    else
+    {
+        // Wait for receives only
+        UPstream::waitRequests(recvRequests.start(), recvRequests.size());
+    }
+
+    double waited = waitTiming.timeIncrement();
+    if (waited > 1e-3)
+    {
+        Pout<< "waited: " << waited << " before processing" << endl;
+    }
+
+    forAll(recvBuffers, proci)
+    {
+        const auto& slice = recvBuffers[proci];
+
+        if (!slice.empty())
+        {
+            // Process data from proci
+            Pout<< "proc:" << proci
+                << ' ' << flatOutput(slice) << nl;
+        }
+    }
+}
+
+
+// Polling receive
+template<class Type>
+void pollingReceive
+(
+    const labelRange& recvRequests,
+    const UList<int>& recvProcs,
+    const List<List<Type>>& recvBuffers
+)
+{
+    clockTime waitTiming;
+
+    DynamicList<int> indices(recvRequests.size());
+
+    if (!recvRequests.empty()) Pout<< "..." << endl;
+
+    for
+    (
+        label loop = 0;
+        UPstream::waitSomeRequests
+        (
+            recvRequests.start(),
+            recvRequests.size(),
+            &indices
+        );
+        ++loop
+    )
+    {
+        double waited = waitTiming.timeIncrement();
+        if (waited <= 1e-3)
+        {
+            waited = 0;
+        }
+        Pout<< "loop:" << loop
+            << " waited: " << waited
+            << " before processing" << endl;
+
+        for (const int idx : indices)
+        {
+            const int proci = recvProcs[idx];
+            const auto& slice = recvBuffers[proci];
+
+            // Process data from proci
+            Pout<< "loop:" << loop << " polled:" << indices.size()
+                << " proc:" << proci
+                << ' ' << flatOutput(slice) << endl;
+        }
+        Pout<< "..." << endl;
+    }
+}
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+int main(int argc, char *argv[])
+{
+    argList::noCheckProcessorDirectories();
+    argList::addVerboseOption("timings etc");
+    argList::addBoolOption("no-polling", "wait all instead of polling");
+    argList::addBoolOption("wait-all", "wait all instead of polling");
+    argList::addOption("sleep", "s", "change sleep (default: 5)");
+    argList::noCheckProcessorDirectories();
+
+    const label transferSize = 10;
+    label sleepSeconds = 5;
+
+    #include "setRootCase.H"
+
+    args.readIfPresent("sleep", sleepSeconds);
+    const bool waitAll = args.found("wait-all");
+    const bool nonPolling = args.found("no-polling");
+
+    if (!Pstream::parRun())
+    {
+        Info<< "\nWarning: not parallel - skipping further tests\n" << endl;
+        return 0;
+    }
+
+    Info<< "Calling with sleep=" << sleepSeconds
+        << ", polling=" << Switch::name(!nonPolling)
+        << ", wait-all=" << Switch::name(waitAll) << nl;
+
+    labelList sendBuffer;
+    List<labelList> recvBuffers;
+
+    if (UPstream::master())
+    {
+        recvBuffers.resize(UPstream::nProcs());
+    }
+    else
+    {
+        recvBuffers.resize(1);
+    }
+
+    clockTime timing;
+
+    const label startOfRequests = UPstream::nRequests();
+
+    // Setup receives
+    labelRange recvRequests(UPstream::nRequests(), 0);
+    DynamicList<int> recvProcs(UPstream::nProcs());
+
+    if (UPstream::master())
+    {
+        for (const int proci : UPstream::subProcs())
+        {
+            // The rank corresponding to the request
+            recvProcs.push_back(proci);
+            auto& slice = recvBuffers[proci];
+            slice.resize_nocopy(transferSize);
+
+            UIPstream::read
+            (
+                UPstream::commsTypes::nonBlocking,
+                proci,
+                slice
+            );
+        }
+    }
+    else
+    {
+        const int proci = UPstream::masterNo();
+
+        if ((UPstream::myProcNo() % 2) == 0)
+        {
+            recvProcs.push_back(proci);
+            auto& slice = recvBuffers[proci];
+            slice.resize_nocopy(transferSize);
+
+            UIPstream::read
+            (
+                UPstream::commsTypes::nonBlocking,
+                proci,
+                slice
+            );
+        }
+    }
+    // OR: recvRequests.size() = (UPstream::nRequests() - recvRequests.start());
+    recvRequests += recvProcs.size();
+
+
+    labelList overallRecvRequests
+    (
+        UPstream::listGatherValues<label>(recvRequests.size())
+    );
+
+    Info<< "Number of recv requests: "
+        << flatOutput(overallRecvRequests) << nl << nl;
+
+
+    // Setup sends
+    sendBuffer.resize_nocopy(transferSize);
+    sendBuffer = UPstream::myProcNo();
+
+    const auto startBufferSend = [&]() -> void
+    {
+        if (sleepSeconds > 0)
+        {
+            // Dispatch some immediately, others with a delay
+            if ((UPstream::myProcNo() % 2) == 0)
+            {
+                sleep(sleepSeconds);
+            }
+            else if ((UPstream::myProcNo() % 3) == 0)
+            {
+                sleep(1.5*sleepSeconds);
+            }
+        }
+
+        UOPstream::write
+        (
+            UPstream::commsTypes::nonBlocking,
+            UPstream::masterNo(),
+            sendBuffer
+        );
+    };
+
+
+    if (UPstream::master())
+    {
+        for (const int proci : UPstream::subProcs())
+        {
+            if ((UPstream::myProcNo() % 2) == 0)
+            {
+                UOPstream::write
+                (
+                    UPstream::commsTypes::nonBlocking,
+                    proci,
+                    sendBuffer
+                );
+            }
+        }
+    }
+    else if (waitAll)
+    {
+        startBufferSend();
+    }
+
+
+    // Some skulduggery to get a differential in timings...
+
+    const int nloops = (UPstream::master() ? 1 : 2);
+
+    for (int loopi = 0; loopi < nloops; ++loopi)
+    {
+        if (waitAll || nonPolling)
+        {
+            waitingReceive(recvRequests, recvBuffers, waitAll);
+        }
+        else
+        {
+            pollingReceive(recvRequests, recvProcs, recvBuffers);
+        }
+
+        // Timing for processing all the receives
+        if (args.verbose())
+        {
+            Pout<< "receive: " << timing.timeIncrement() << 's' << endl;
+        }
+
+        if (!UPstream::master() && loopi == 0 && !waitAll)
+        {
+            startBufferSend();
+        }
+    }
+
+    if (args.verbose())
+    {
+        Pout<< "timing: " << timing.elapsedTime() << 's' << endl;
+    }
+
+    // Final
+    UPstream::waitRequests(startOfRequests);
+
+    Info<< "End\n" << endl;
+    return 0;
+}
+
+
+// ************************************************************************* //
diff --git a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
index df37286cf7..7d35630177 100644
--- a/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
+++ b/src/OpenFOAM/db/IOstreams/Pstreams/UPstream.H
@@ -604,6 +604,17 @@ public:
         //  A no-op if parRun() == false or list is empty
         static void cancelRequests(UList<UPstream::Request>& requests);
 
+        //- Non-blocking comms: cancel/free outstanding requests
+        //- (from position onwards) and remove from internal list of requests.
+        //- Corresponds to MPI_Cancel() + MPI_Request_free()
+        //  A no-op if parRun() == false,
+        //  if the position is out-of-range [0 to nRequests()],
+        //  or the internal list of requests is empty.
+        //
+        //  \param pos starting position within the internal list of requests
+        //  \param len length of slice to remove (negative = until the end)
+        static void removeRequests(const label pos, label len = -1);
+
         //- Non-blocking comms: free outstanding request.
         //- Corresponds to MPI_Request_free()
         //  A no-op if parRun() == false
@@ -656,13 +667,32 @@ public:
         //  \returns false if all requests have already been handled
         //
         //  \param pos starting position within the internal list of requests
+        //  \param len length of slice to check (negative = until the end)
         //  \param[out] indices the completed request indices relative to the
-        //      starting position. The is an optional parameter, which can be
+        //      starting position. This is an optional parameter that can be
         //      used to recover the indices or simply to avoid reallocations
         //      when calling within a loop.
         static bool waitSomeRequests
         (
             const label pos,
+            label len = -1,
+            DynamicList<int>* indices = nullptr
+        );
+
+        //- Wait until some requests have finished.
+        //- Corresponds to MPI_Waitsome()
+        //  A no-op and returns false if parRun() == false,
+        //  the list is empty,
+        //  or if all the requests have already been handled.
+        //
+        //  \param requests the requests
+        //  \param[out] indices the completed request indices relative to the
+        //      starting position. This is an optional parameter that can be
+        //      used to recover the indices or simply to avoid reallocations
+        //      when calling within a loop.
+        static bool waitSomeRequests
+        (
+            UList<UPstream::Request>& requests,
             DynamicList<int>* indices = nullptr
         );
 
diff --git a/src/OpenFOAM/matrices/LduMatrix/LduMatrix/LduMatrixUpdateMatrixInterfaces.C b/src/OpenFOAM/matrices/LduMatrix/LduMatrix/LduMatrixUpdateMatrixInterfaces.C
index 2bf5f533fe..a3fa3d2bb1 100644
--- a/src/OpenFOAM/matrices/LduMatrix/LduMatrix/LduMatrixUpdateMatrixInterfaces.C
+++ b/src/OpenFOAM/matrices/LduMatrix/LduMatrix/LduMatrixUpdateMatrixInterfaces.C
@@ -134,7 +134,7 @@ void Foam::LduMatrix<Type, DType, LUType>::updateMatrixInterfaces
             bool pollingActive = (UPstream::nPollProcInterfaces < 0);
             (
                 pollingActive
-             && UPstream::waitSomeRequests(startRequest, &indices)
+             && UPstream::waitSomeRequests(startRequest, -1, &indices)
             );
             /*nil*/
         )
diff --git a/src/OpenFOAM/matrices/lduMatrix/lduMatrix/lduMatrixUpdateMatrixInterfaces.C b/src/OpenFOAM/matrices/lduMatrix/lduMatrix/lduMatrixUpdateMatrixInterfaces.C
index 17fbdc6043..b7434b7e1a 100644
--- a/src/OpenFOAM/matrices/lduMatrix/lduMatrix/lduMatrixUpdateMatrixInterfaces.C
+++ b/src/OpenFOAM/matrices/lduMatrix/lduMatrix/lduMatrixUpdateMatrixInterfaces.C
@@ -144,7 +144,7 @@ void Foam::lduMatrix::updateMatrixInterfaces
             bool pollingActive = (UPstream::nPollProcInterfaces < 0);
             (
                 pollingActive
-             && UPstream::waitSomeRequests(startRequest, &indices)
+             && UPstream::waitSomeRequests(startRequest, -1, &indices)
             );
             /*nil*/
         )
diff --git a/src/Pstream/dummy/UPstreamRequest.C b/src/Pstream/dummy/UPstreamRequest.C
index f4962ffd45..dd56a0569d 100644
--- a/src/Pstream/dummy/UPstreamRequest.C
+++ b/src/Pstream/dummy/UPstreamRequest.C
@@ -59,6 +59,8 @@ void Foam::UPstream::cancelRequest(const label i) {}
 void Foam::UPstream::cancelRequest(UPstream::Request&) {}
 void Foam::UPstream::cancelRequests(UList<UPstream::Request>&) {}
 
+void Foam::UPstream::removeRequests(const label pos, label len) {}
+
 void Foam::UPstream::freeRequest(UPstream::Request&) {}
 void Foam::UPstream::freeRequests(UList<UPstream::Request>&) {}
 
@@ -73,6 +75,17 @@ bool Foam::UPstream::waitAnyRequest(const label pos, label len)
 bool Foam::UPstream::waitSomeRequests
 (
     const label pos,
+    label len,
+    DynamicList<int>* indices
+)
+{
+    if (indices) indices->clear();
+    return false;
+}
+
+bool Foam::UPstream::waitSomeRequests
+(
+    UList<UPstream::Request>& requests,
     DynamicList<int>* indices
 )
 {
diff --git a/src/Pstream/mpi/UPstreamRequest.C b/src/Pstream/mpi/UPstreamRequest.C
index 4f9467fd22..ec773ec106 100644
--- a/src/Pstream/mpi/UPstreamRequest.C
+++ b/src/Pstream/mpi/UPstreamRequest.C
@@ -153,6 +153,47 @@ void Foam::UPstream::cancelRequests(UList<UPstream::Request>& requests)
 }
 
 
+void Foam::UPstream::removeRequests(const label pos, label len)
+{
+    // No-op for non-parallel, no pending requests or out-of-range
+    if
+    (
+        !UPstream::parRun()
+     || (pos < 0 || pos >= PstreamGlobals::outstandingRequests_.size())
+     || !len
+    )
+    {
+        return;
+    }
+
+    label count = (PstreamGlobals::outstandingRequests_.size() - pos);
+
+    // Apply range-checking on slice with (len < 0) behaving like npos
+    // (ie, the rest of the list)
+    if (len >= 0 && len < count)
+    {
+        // A non-trailing slice
+        count = len;
+    }
+    // Have count >= 1
+
+    const labelRange range(pos, count);
+
+    for (const label i : range)
+    {
+        auto& request = PstreamGlobals::outstandingRequests_[i];
+        if (MPI_REQUEST_NULL != request)  // Active handle is mandatory
+        {
+            MPI_Cancel(&request);
+            MPI_Request_free(&request);  //<- Sets to MPI_REQUEST_NULL
+        }
+    }
+
+    // Remove from list of outstanding requests and move down
+    PstreamGlobals::outstandingRequests_.remove(range);
+}
+
+
 void Foam::UPstream::freeRequest(UPstream::Request& req)
 {
     // No-op for non-parallel
@@ -214,7 +255,7 @@ void Foam::UPstream::waitRequests(const label pos, label len)
     }
 
     label count = (PstreamGlobals::outstandingRequests_.size() - pos);
-    bool trim = true;  // Trim the trailing part of the list
+    bool trim = true;  // Can trim the trailing part of the list
 
     // Apply range-checking on slice with (len < 0) behaving like npos
     // (ie, the rest of the list)
@@ -348,7 +389,7 @@ bool Foam::UPstream::waitAnyRequest(const label pos, label len)
 
     if (UPstream::debug)
     {
-        Pout<< "UPstream::waitAnyRequest : starting wait for some of "
+        Pout<< "UPstream::waitAnyRequest : starting wait for any of "
             << count << " requests starting at " << pos << endl;
     }
 
@@ -378,6 +419,7 @@ bool Foam::UPstream::waitAnyRequest(const label pos, label len)
 bool Foam::UPstream::waitSomeRequests
 (
     const label pos,
+    label len,
     DynamicList<int>* indices
 )
 {
@@ -386,13 +428,10 @@ bool Foam::UPstream::waitSomeRequests
     (
         !UPstream::parRun()
      || (pos < 0 || pos >= PstreamGlobals::outstandingRequests_.size())
-     // || !len
+     || !len
     )
     {
-        if (indices)
-        {
-            indices->clear();
-        }
+        if (indices) indices->clear();
         return false;
     }
 
@@ -400,25 +439,24 @@ bool Foam::UPstream::waitSomeRequests
 
     // Apply range-checking on slice with (len < 0) behaving like npos
     // (ie, the rest of the list)
-    // if (len >= 0 && len < count)
-    // {
-    //     // A non-trailing slice
-    //     count = len;
-    // }
+    if (len >= 0 && len < count)
+    {
+        // A non-trailing slice
+        count = len;
+    }
     // Have count >= 1
 
     auto* waitRequests = (PstreamGlobals::outstandingRequests_.data() + pos);
 
     if (UPstream::debug)
     {
-        Pout<< "UPstream:waitSomeRequest : starting wait for any of "
+        Pout<< "UPstream:waitSomeRequest : starting wait for some of "
             << count << " requests starting at " << pos << endl;
     }
 
 
     // Local temporary storage, or return via calling parameter
     List<int> tmpIndices;
-
     if (indices)
     {
         indices->resize_nocopy(count);
@@ -454,10 +492,7 @@ bool Foam::UPstream::waitSomeRequests
     if (outcount == MPI_UNDEFINED || outcount < 1)
     {
         // No active request handles
-        if (indices)
-        {
-            indices->clear();
-        }
+        if (indices) indices->clear();
         return false;
     }
 
@@ -470,6 +505,99 @@ bool Foam::UPstream::waitSomeRequests
 }
 
 
+bool Foam::UPstream::waitSomeRequests
+(
+    UList<UPstream::Request>& requests,
+    DynamicList<int>* indices
+)
+{
+    // No-op for non-parallel or no pending requests
+    if (!UPstream::parRun() || requests.empty())
+    {
+        if (indices) indices->clear();
+        return false;
+    }
+
+    // Looks ugly but is legitimate since UPstream::Request is an intptr_t,
+    // which is always large enough to hold an MPI_Request (int or pointer)
+
+    label count = 0;
+    auto* waitRequests = reinterpret_cast<MPI_Request*>(requests.data());
+
+    for (auto& req : requests)
+    {
+        waitRequests[count] = PstreamDetail::Request::get(req);
+        ++count;
+    }
+
+    // Local temporary storage, or return via calling parameter
+    List<int> tmpIndices;
+    if (indices)
+    {
+        indices->resize_nocopy(count);
+    }
+    else
+    {
+        tmpIndices.resize(count);
+    }
+
+    if (UPstream::debug)
+    {
+        Pout<< "UPstream:waitSomeRequest : starting wait for some of "
+            << requests.size() << " requests" << endl;
+    }
+
+    profilingPstream::beginTiming();
+
+    // On success: sets non-blocking requests to MPI_REQUEST_NULL
+    int outcount = 0;
+    if
+    (
+        MPI_Waitsome
+        (
+            count,
+            waitRequests,
+           &outcount,
+            (indices ? indices->data() : tmpIndices.data()),
+            MPI_STATUSES_IGNORE
+        )
+    )
+    {
+        FatalErrorInFunction
+            << "MPI_Waitsome returned with error"
+            << Foam::abort(FatalError);
+    }
+
+    profilingPstream::addWaitTime();
+
+    if (outcount == MPI_UNDEFINED || outcount < 1)
+    {
+        // No active request handles
+        if (indices) indices->clear();
+
+        // Everything handled or inactive, reset all to MPI_REQUEST_NULL
+        requests = UPstream::Request(MPI_REQUEST_NULL);
+        return false;
+    }
+
+    if (indices)
+    {
+        indices->resize(outcount);
+    }
+
+    // Transcribe MPI_Request back into UPstream::Request
+    // - do in reverse order - see note in finishedRequests()
+    {
+        for (label i = requests.size()-1; i >= 0; --i)
+        {
+            requests[i] = UPstream::Request(waitRequests[i]);
+        }
+    }
+
+    return true;
+}
+
+
 Foam::label Foam::UPstream::waitAnyRequest(UList<UPstream::Request>& requests)
 {
     // No-op for non-parallel or no pending requests