diff --git a/src/main.rs b/src/main.rs
index c1f6fd2..7241eed 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -74,6 +74,10 @@ struct Args {
     #[arg(long = "no-progress", global = true)]
     no_progress: bool,
 
+    /// Number of concurrent worker jobs to use when processing independent inputs.
+    #[arg(short = 'j', long = "jobs", value_name = "N", default_value_t = 1, global = true)]
+    jobs: usize,
+
     /// Optional auxiliary subcommands (completions, man)
     #[command(subcommand)]
     aux: Option<AuxCommands>,
@@ -386,42 +390,113 @@ fn run() -> Result<()> {
     let start_overall = Instant::now();
 
     if do_merge {
-        for (i, (path, speaker)) in plan.iter().enumerate() {
-            let start = Instant::now();
-            if !path.exists() {
-                had_error = true;
-                summary.push((
-                    path.file_name().and_then(|s| s.to_str().map(|s| s.to_string())).unwrap_or_else(|| path.to_string_lossy().to_string()),
-                    speaker.clone(),
-                    false,
-                    start.elapsed(),
-                ));
-                if !args.continue_on_error {
-                    break;
+        // Setup progress
+        pm.set_total(plan.len());
+
+        use std::sync::{Arc, atomic::{AtomicUsize, Ordering}};
+        use std::thread;
+        use std::sync::mpsc;
+
+        // Results channel: workers send Started and Finished events to main thread
+        enum Msg {
+            Started(usize, String),
+            Finished(usize, Result<(Vec<InputSegment>, String /*disp_name*/, bool /*ok*/ , ::std::time::Duration)>),
+        }
+
+        let (tx, rx) = mpsc::channel::<Msg>();
+        let next = Arc::new(AtomicUsize::new(0));
+        let jobs = args.jobs.max(1).min(plan.len().max(1));
+
+        let plan_arc: Arc<Vec<(PathBuf, String)>> = Arc::new(plan.clone());
+
+        let mut workers = Vec::new();
+        for _ in 0..jobs {
+            let tx = tx.clone();
+            let next = Arc::clone(&next);
+            let plan = Arc::clone(&plan_arc);
+            let read_json_file = read_json_file; // move fn item
+            workers.push(thread::spawn(move || {
+                loop {
+                    let idx = next.fetch_add(1, Ordering::SeqCst);
+                    if idx >= plan.len() { break; }
+                    let (path, speaker) = (&plan[idx].0, &plan[idx].1);
+                    // Notify started (use display name)
+                    let disp = path.file_name().and_then(|s| s.to_str()).map(|s| s.to_string()).unwrap_or_else(|| path.to_string_lossy().to_string());
+                    let _ = tx.send(Msg::Started(idx, disp.clone()));
+                    let start = Instant::now();
+                    // Process only JSON and existence checks here
+                    let res: Result<(Vec<InputSegment>, String, bool, ::std::time::Duration)> = (|| {
+                        if !path.exists() {
+                            return Ok((Vec::new(), disp.clone(), false, start.elapsed()));
+                        }
+                        if is_json_file(path) {
+                            let root = read_json_file(path)?;
+                            Ok((root.segments, disp.clone(), true, start.elapsed()))
+                        } else if is_audio_file(path) {
+                            // Audio path not implemented here for parallel read; handle later if needed
+                            Ok((Vec::new(), disp.clone(), true, start.elapsed()))
+                        } else {
+                            // Unknown type: mark as error
+                            Ok((Vec::new(), disp.clone(), false, start.elapsed()))
+                        }
+                    })();
+                    let _ = tx.send(Msg::Finished(idx, res));
+                }
+            }));
+        }
+        drop(tx); // close original sender
+
+        // Collect results deterministically by index; assign IDs sequentially after all complete
+        let mut per_file: Vec<Option<(Vec<InputSegment>, String /*disp_name*/, bool, ::std::time::Duration)>> = (0..plan.len()).map(|_| None).collect();
+        let mut remaining = plan.len();
+        while let Ok(msg) = rx.recv() {
+            match msg {
+                Msg::Started(_idx, label) => {
+                    // Update spinner to show most recently started file
+                    let _ih = pm.start_item(&label);
+                }
+                Msg::Finished(idx, res) => {
+                    match res {
+                        Ok((segments, disp, ok, dur)) => {
+                            per_file[idx] = Some((segments, disp, ok, dur));
+                        }
+                        Err(e) => {
+                            // Treat as failure for this file; store empty segments
+                            per_file[idx] = Some((Vec::new(), format!("{}", e), false, ::std::time::Duration::from_millis(0)));
+                        }
+                    }
+                    pm.inc_completed();
+                    remaining -= 1;
+                    if remaining == 0 { break; }
                 }
-                continue;
             }
-            if is_json_file(path) {
-                let root = read_json_file(path)?;
-                for (idx, seg) in root.segments.iter().enumerate() {
+        }
+        // Join workers
+        for w in workers { let _ = w.join(); }
+
+        // Now, sequentially assign final IDs in input order
+        for (i, maybe) in per_file.into_iter().enumerate() {
+            let (segments, disp, ok, dur) = maybe.unwrap_or((Vec::new(), String::new(), false, ::std::time::Duration::from_millis(0)));
+            let (_path, speaker) = (&plan[i].0, &plan[i].1);
+            if ok {
+                for seg in segments {
                     merged_items.push(polyscribe::OutputEntry {
-                        id: (merged_items.len() as u64),
+                        id: merged_items.len() as u64,
                         speaker: speaker.clone(),
                         start: seg.start,
                         end: seg.end,
-                        text: seg.text.clone(),
+                        text: seg.text,
                     });
                 }
-            } else if is_audio_file(path) {
-                // Not exercised by tests; skip for now.
+            } else {
+                had_error = true;
+                if !args.continue_on_error {
+                    // If not continuing, stop building and reflect failure below
+                }
             }
-            summary.push((
-                path.file_name().and_then(|s| s.to_str().map(|s| s.to_string())).unwrap_or_else(|| path.to_string_lossy().to_string()),
-                speaker.clone(),
-                true,
-                start.elapsed(),
-            ));
-            let _ = i; // silence unused in case
+            // push summary deterministic by input index
+            summary.push((disp, speaker.clone(), ok, dur));
+            if !ok && !args.continue_on_error { break; }
         }
 
         // Write merged outputs
diff --git a/tests/deterministic_jobs.rs b/tests/deterministic_jobs.rs
new file mode 100644
index 0000000..f2fa32a
--- /dev/null
+++ b/tests/deterministic_jobs.rs
@@ -0,0 +1,62 @@
+use std::ffi::OsStr;
+use std::process::{Command, Stdio};
+use std::time::Duration;
+
+fn bin() -> &'static str {
+    env!("CARGO_BIN_EXE_polyscribe")
+}
+
+fn manifest_path(rel: &str) -> std::path::PathBuf {
+    let mut p = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    p.push(rel);
+    p
+}
+
+fn run_polyscribe<I, S>(args: I, timeout: Duration) -> std::io::Result<std::process::Output>
+where
+    I: IntoIterator<Item = S>,
+    S: AsRef<OsStr>,
+{
+    let mut child = Command::new(bin())
+        .args(args)
+        .stdin(Stdio::null())
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
+        .env_clear()
+        .env("CI", "1")
+        .env("NO_COLOR", "1")
+        .spawn()?;
+
+    let start = std::time::Instant::now();
+    loop {
+        if let Some(status) = child.try_wait()? {
+            let mut out = std::process::Output { status, stdout: Vec::new(), stderr: Vec::new() };
+            if let Some(mut s) = child.stdout.take() { let _ = std::io::copy(&mut s, &mut out.stdout); }
+            if let Some(mut s) = child.stderr.take() { let _ = std::io::copy(&mut s, &mut out.stderr); }
+            return Ok(out);
+        }
+        if start.elapsed() >= timeout {
+            let _ = child.kill();
+            let _ = child.wait();
+            return Err(std::io::Error::new(std::io::ErrorKind::TimedOut, "polyscribe timed out"));
+        }
+        std::thread::sleep(std::time::Duration::from_millis(10))
+    }
+}
+
+#[test]
+fn merge_output_is_deterministic_across_job_counts() {
+    let input1 = manifest_path("input/1-s0wlz.json");
+    let input2 = manifest_path("input/2-vikingowl.json");
+
+    let out_j1 = run_polyscribe(&[input1.as_os_str(), input2.as_os_str(), OsStr::new("-m"), OsStr::new("--jobs"), OsStr::new("1")], Duration::from_secs(30)).expect("run jobs=1");
+    assert!(out_j1.status.success(), "jobs=1 failed, stderr: {}", String::from_utf8_lossy(&out_j1.stderr));
+
+    let out_j4 = run_polyscribe(&[input1.as_os_str(), input2.as_os_str(), OsStr::new("-m"), OsStr::new("--jobs"), OsStr::new("4")], Duration::from_secs(30)).expect("run jobs=4");
+    assert!(out_j4.status.success(), "jobs=4 failed, stderr: {}", String::from_utf8_lossy(&out_j4.stderr));
+
+    let s1 = String::from_utf8(out_j1.stdout).expect("utf8");
+    let s4 = String::from_utf8(out_j4.stdout).expect("utf8");
+
+    assert_eq!(s1, s4, "merged JSON stdout differs between jobs=1 and jobs=4");
+}