diff --git a/tests/bin/emit1_cohttp.ml b/tests/bin/emit1_cohttp.ml
index 0611c754..14f657cd 100644
--- a/tests/bin/emit1_cohttp.ml
+++ b/tests/bin/emit1_cohttp.ml
@@ -109,6 +109,7 @@ let () =
   let batch_metrics = ref 3 in
   let batch_logs = ref 400 in
   let url = ref None in
+  let n_procs = ref 1 in
   let opts =
     [
       "--debug", Arg.Bool (( := ) debug), " enable debug output";
@@ -127,12 +128,18 @@ let () =
       "--sleep-outer", Arg.Set_float sleep_outer, " sleep (in s) in outer loop";
       "--iterations", Arg.Set_int iterations, " the number of iterations to run";
       "-j", Arg.Set_int n_jobs, " number of parallel jobs";
+      "--procs", Arg.Set_int n_procs, " number of processes";
     ]
     |> Arg.align
   in
 
   Arg.parse opts (fun _ -> ()) "emit1 [opt]*";
 
+  if !n_procs > 1 then
+    failwith
+      "TODO: add support for running multiple processes to the lwt-cohttp \
+       emitter";
+
   let some_if_nzero r =
     if !r > 0 then
       Some !r
diff --git a/tests/bin/emit1_eio.ml b/tests/bin/emit1_eio.ml
index dc5198ae..debb9e75 100644
--- a/tests/bin/emit1_eio.ml
+++ b/tests/bin/emit1_eio.ml
@@ -11,7 +11,7 @@ let sleep_outer = ref 2.0
 
 let n_jobs = ref 1
 
-let iterations = ref 1
+let iterations = Atomic.make 1
 
 let num_sleep = Atomic.make 0
 
@@ -32,8 +32,8 @@ let run_job clock _job_id : unit =
         ~attrs:[ "i", `Int !i ]
     in
 
-    for j = 0 to !iterations do
-      if j >= !iterations then
+    for j = 0 to Atomic.get iterations do
+      if j >= Atomic.get iterations then
         (* Terminate program, having reached our max iterations *)
         Atomic.set stop true
       else
@@ -80,7 +80,7 @@ let run_job clock _job_id : unit =
     done
   done
 
-let run env : unit =
+let run env proc () : unit =
   OT.GC_metrics.basic_setup ();
 
   OT.Metrics_callbacks.register (fun () ->
@@ -91,7 +91,7 @@ let run env : unit =
         ]);
 
   let n_jobs = max 1 !n_jobs in
-  Printf.printf "run %d jobs\n%!" n_jobs;
+  Printf.printf "run %d jobs in proc %d\n%!" n_jobs proc;
 
   Eio.Switch.run (fun sw ->
       for j = 1 to n_jobs do
@@ -109,6 +109,7 @@ let () =
   let batch_metrics = ref 3 in
   let batch_logs = ref 400 in
   let url = ref None in
+  let n_procs = ref 1 in
   let opts =
     [
       "--debug", Arg.Bool (( := ) debug), " enable debug output";
@@ -125,8 +126,11 @@ let () =
       "--batch-logs", Arg.Int (( := ) batch_logs), " size of logs batch";
       "--sleep-inner", Arg.Set_float sleep_inner, " sleep (in s) in inner loop";
       "--sleep-outer", Arg.Set_float sleep_outer, " sleep (in s) in outer loop";
-      "--iterations", Arg.Set_int iterations, " the number of iterations to run";
-      "-j", Arg.Set_int n_jobs, " number of parallel jobs";
+      ( "--iterations",
+        Arg.Int (Atomic.set iterations),
+        " the number of iterations to run" );
+      "-j", Arg.Set_int n_jobs, " number of jobs per processes";
+      "--procs", Arg.Set_int n_procs, " number of processes";
     ]
     |> Arg.align
   in
@@ -155,4 +159,16 @@ let () =
         Printf.printf "\ndone. %d spans in %.4fs (%.4f/s)\n%!"
           (Atomic.get num_tr) elapsed n_per_sec)
   in
-  Opentelemetry_client_cohttp_eio.with_setup ~stop ~config run |> Eio_main.run
+  Eio_main.run @@ fun env ->
+  (if !n_procs < 2 then
+     Opentelemetry_client_cohttp_eio.with_setup ~stop ~config (run env 0) env
+   else
+     Eio.Switch.run @@ fun sw ->
+     Opentelemetry_client_cohttp_eio.setup ~stop ~config ~sw env;
+     let dm = Eio.Stdenv.domain_mgr env in
+     Eio.Switch.run (fun sw ->
+         for proc = 1 to !n_procs do
+           Eio.Fiber.fork ~sw @@ fun () ->
+           Eio.Domain_manager.run dm (run env proc)
+         done));
+  Opentelemetry.Collector.remove_backend () ~on_done:ignore
diff --git a/tests/client_e2e/clients_e2e_lib.ml b/tests/client_e2e/clients_e2e_lib.ml
index 8c085a22..3206bfe9 100644
--- a/tests/client_e2e/clients_e2e_lib.ml
+++ b/tests/client_e2e/clients_e2e_lib.ml
@@ -56,6 +56,15 @@ let filter_map_metrics f signals =
          |> List.find_map (fun ss ->
                 ss.Proto.Metrics.metrics |> List.find_map f))
 
+let count_metrics_with_name name signals =
+  signals
+  |> filter_map_metrics (fun s ->
+         if String.equal s.Proto.Metrics.name name then
+           Some s
+         else
+           None)
+  |> List.length
+
 let number_data_point_to_float : Proto.Metrics.number_data_point_value -> float
     = function
   | Proto.Metrics.As_double f -> f
@@ -98,6 +107,7 @@ let count_logs_with_body p signals =
 type params = {
   url: string;
   jobs: int;
+  procs: int;
   batch_traces: int;
   batch_metrics: int;
   batch_logs: int;
@@ -109,6 +119,8 @@ let cmd exec params =
     exec;
     "-j";
     string_of_int params.jobs;
+    "--procs";
+    string_of_int params.procs;
     "--url";
     params.url;
     "--iterations";
@@ -134,22 +146,24 @@ let tests params signal_batches =
     (* TODO: What properties of batch sizes does it make sense to test? *)
     test "loop.outer spans" (fun () ->
         Alcotest.(check' int)
-          ~msg:"number of occurrences should equal the configured jobs"
-          ~expected:params.jobs
+          ~msg:
+            "number of occurrences should equal the configured jobs * the \
+             configured processes"
+          ~expected:(params.jobs * params.procs)
           ~actual:(count_spans_with_name "loop.outer" signals));
     test "loop.inner spans" (fun () ->
         Alcotest.(check' int)
           ~msg:
             "number of occurrences should equal the configured jobs * the  \
-             configured iterations"
-          ~expected:(params.jobs * params.iterations)
+             configured iterations * configured processes"
+          ~expected:(params.jobs * params.iterations * params.procs)
           ~actual:(count_spans_with_name "loop.inner" signals));
     test "alloc spans" (fun () ->
         Alcotest.(check' int)
           ~msg:
             "number of occurrences should equal the configured jobs * the  \
-             configured iterations"
-          ~expected:(params.jobs * params.iterations)
+             configured iterations * configured processes"
+          ~expected:(params.jobs * params.iterations * params.procs)
           ~actual:(count_spans_with_name "alloc" signals);
         Alcotest.(check' bool)
           ~msg:"should have 'done with alloc' event" ~expected:true
@@ -167,16 +181,19 @@ let tests params signal_batches =
              |> List.for_all (fun (e : Proto.Trace.span_event) ->
                     String.equal e.name "done with alloc")));
     test "num-sleep metrics" (fun () ->
-        Alcotest.(check' (float 0.))
-          ~msg:"should record jobs * iterations sleeps"
-          ~expected:(params.jobs * params.iterations |> float_of_int)
+        Alcotest.(check' bool)
+          ~msg:
+            "should record at lest as many sleep metrics as there are \
+             iterations configured"
+          ~expected:true
           ~actual:
-            (get_metric_values "num-sleep" signals
-            |> List.sort Float.compare |> List.rev |> List.hd));
+            (count_metrics_with_name "num-sleep" signals >= params.iterations));
     test "logs" (fun () ->
         Alcotest.(check' int)
-          ~msg:"should record jobs * iterations occurrences of 'inner at n'"
-          ~expected:(params.jobs * params.iterations)
+          ~msg:
+            "should record jobs * iterations occurrences * configured \
+             processes of 'inner at n'"
+          ~expected:(params.jobs * params.iterations * params.procs)
           ~actual:
             (signals
             |> count_logs_with_body (function
diff --git a/tests/client_e2e/test_cottp_eio_client_e2e.ml b/tests/client_e2e/test_cottp_eio_client_e2e.ml
index 539a1ba4..ab5cf985 100644
--- a/tests/client_e2e/test_cottp_eio_client_e2e.ml
+++ b/tests/client_e2e/test_cottp_eio_client_e2e.ml
@@ -15,6 +15,7 @@ let () =
         {
           url;
           jobs = 1;
+          procs = 1;
           iterations = 1;
           batch_traces = 2;
           batch_metrics = 2;
@@ -24,6 +25,17 @@ let () =
         {
           url;
           jobs = 3;
+          procs = 1;
+          iterations = 1;
+          batch_traces = 400;
+          batch_metrics = 3;
+          batch_logs = 400;
+        } );
+      ( "emit1_eio",
+        {
+          url;
+          jobs = 3;
+          procs = 3;
           iterations = 1;
           batch_traces = 400;
           batch_metrics = 3;
diff --git a/tests/client_e2e/test_cottp_lwt_client_e2e.ml b/tests/client_e2e/test_cottp_lwt_client_e2e.ml
index 5c72165e..b1ba3772 100644
--- a/tests/client_e2e/test_cottp_lwt_client_e2e.ml
+++ b/tests/client_e2e/test_cottp_lwt_client_e2e.ml
@@ -25,6 +25,7 @@ let () =
         {
           url;
           jobs = 1;
+          procs = 1;
           iterations = 1;
           batch_traces = 2;
           batch_metrics = 2;
@@ -34,6 +35,7 @@ let () =
         {
           url;
           jobs = 3;
+          procs = 1;
           iterations = 1;
           batch_traces = 400;
           batch_metrics = 3;