diff --git a/calculate_average_J-Sek.sh b/calculate_average_J-Sek.sh
new file mode 100755
index 0000000..d802d59
--- /dev/null
+++ b/calculate_average_J-Sek.sh
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+time bun run src/main/bun/J-Sek/index.ts measurements.txt
diff --git a/src/main/bun/J-Sek/.gitignore b/src/main/bun/J-Sek/.gitignore
new file mode 100644
index 0000000..22d8f1d
--- /dev/null
+++ b/src/main/bun/J-Sek/.gitignore
@@ -0,0 +1,177 @@
+# Based on https://raw.githubusercontent.com/github/gitignore/main/Node.gitignore
+
+# Logs
+
+logs
+_.log
+npm-debug.log_
+yarn-debug.log*
+yarn-error.log*
+lerna-debug.log*
+.pnpm-debug.log*
+
+# Caches 
+
+.cache
+
+# Diagnostic reports (https://nodejs.org/api/report.html)
+
+report.[0-9]_.[0-9]_.[0-9]_.[0-9]_.json
+
+# Runtime data
+
+pids
+_.pid
+_.seed
+*.pid.lock
+
+# Directory for instrumented libs generated by jscoverage/JSCover
+
+lib-cov
+
+# Coverage directory used by tools like istanbul
+
+coverage
+*.lcov
+
+# nyc test coverage
+
+.nyc_output
+
+# Grunt intermediate storage (https://gruntjs.com/creating-plugins#storing-task-files)
+
+.grunt
+
+# Bower dependency directory (https://bower.io/)
+
+bower_components
+
+# node-waf configuration
+
+.lock-wscript
+
+# Compiled binary addons (https://nodejs.org/api/addons.html)
+
+build/Release
+
+# Dependency directories
+
+node_modules/
+jspm_packages/
+
+# Snowpack dependency directory (https://snowpack.dev/)
+
+web_modules/
+
+# TypeScript cache
+
+*.tsbuildinfo
+
+# Optional npm cache directory
+
+.npm
+
+# Optional eslint cache
+
+.eslintcache
+
+# Optional stylelint cache
+
+.stylelintcache
+
+# Microbundle cache
+
+.rpt2_cache/
+.rts2_cache_cjs/
+.rts2_cache_es/
+.rts2_cache_umd/
+
+# Optional REPL history
+
+.node_repl_history
+
+# Output of 'npm pack'
+
+*.tgz
+
+# Yarn Integrity file
+
+.yarn-integrity
+
+# dotenv environment variable files
+
+.env
+.env.development.local
+.env.test.local
+.env.production.local
+.env.local
+
+# parcel-bundler cache (https://parceljs.org/)
+
+.parcel-cache
+
+# Next.js build output
+
+.next
+out
+
+# Nuxt.js build / generate output
+
+.nuxt
+dist
+
+# Gatsby files
+
+# Comment in the public line in if your project uses Gatsby and not Next.js
+
+# https://nextjs.org/blog/next-9-1#public-directory-support
+
+# public
+
+# vuepress build output
+
+.vuepress/dist
+
+# vuepress v2.x temp and cache directory
+
+.temp
+
+# Docusaurus cache and generated files
+
+.docusaurus
+
+# Serverless directories
+
+.serverless/
+
+# FuseBox cache
+
+.fusebox/
+
+# DynamoDB Local files
+
+.dynamodb/
+
+# TernJS port file
+
+.tern-port
+
+# Stores VSCode versions used for testing VSCode extensions
+
+.vscode-test
+
+# yarn v2
+
+.yarn/cache
+.yarn/unplugged
+.yarn/build-state.yml
+.yarn/install-state.gz
+.pnp.*
+
+# IntelliJ based IDEs
+.idea
+
+# Finder (MacOS) folder config
+.DS_Store
+
+bun.lockb
diff --git a/src/main/bun/J-Sek/README.md b/src/main/bun/J-Sek/README.md
new file mode 100644
index 0000000..b8ecba6
--- /dev/null
+++ b/src/main/bun/J-Sek/README.md
@@ -0,0 +1,15 @@
+# 1brc
+
+To install dependencies:
+
+```bash
+bun install
+```
+
+To run:
+
+```bash
+bun run index.ts
+```
+
+This project was created using `bun init` in bun v1.0.21. [Bun](https://bun.sh) is a fast all-in-one JavaScript runtime.
diff --git a/src/main/bun/J-Sek/index.ts b/src/main/bun/J-Sek/index.ts
new file mode 100644
index 0000000..ad7d347
--- /dev/null
+++ b/src/main/bun/J-Sek/index.ts
@@ -0,0 +1,90 @@
+import * as os from "node:os";
+import { createReadStream } from "node:fs";
+
+const fileName = Bun.argv[2];
+
+const fileSize = Bun.file(fileName).size;
+
+const workerCount = os.cpus().length - 1;
+
+let lastOffset = 0;
+const tasks = [];
+while (lastOffset < fileSize) {
+  const start = lastOffset;
+  let end = Math.min(fileSize, start + 100 + fileSize / workerCount);
+  if (end < fileSize) {
+    end = await moveToClosestLineBreak(end);
+  }
+  tasks.push(
+    new Promise<Map<string, CityValues>>((resolve, reject) => {
+      const worker = new Worker(new URL("worker.ts", import.meta.url).href);
+      worker.postMessage({ fileName, start, end });
+      worker.onmessage = (e) => resolve(e.data);
+      worker.onerror = (e) => { console.error(e); reject(); };
+    })
+  );
+  lastOffset = end;
+}
+
+const groups = await Promise.all(tasks);
+const cities = aggregate(groups);
+printResults();
+
+type CityValues = { min: number; max: number; avg: number; count: number };
+
+function aggregate(groups: Map<string, CityValues>[]) {
+  const [firstGroup, ...rest] = groups;
+  const allCities = firstGroup;
+
+  rest.forEach(g => {
+    [...g.entries()].forEach(([city, gv]) => {
+      if (!allCities.has(city)) {
+        allCities.set(city, gv);
+      } else {
+        const values = allCities.get(city)!;
+        if (values.min > gv.min) values.min = gv.min;
+        if (values.max < gv.max) values.max = gv.max;
+        const newCount = values.count + gv.count;
+        if ((values.count + gv.count) < (Number.MAX_VALUE / 100)) {
+          // hack in condition above to avoid int overflow
+          values.avg = (values.avg * values.count + gv.avg * gv.count) / newCount;
+          values.count = newCount;
+        }
+      }
+    })
+  })
+
+  return allCities;
+}
+
+function printResults() {
+  const result =
+    "{" +
+    [...cities.keys()]
+      .toSorted()
+      .map((city) => {
+        const values = cities.get(city)!;
+        const out = [
+          values.min.toFixed(1),
+          values.avg.toFixed(1),
+          values.max.toFixed(1),
+        ].join("/");
+        return [city, out].join("=");
+      })
+      .join(", ") +
+    "}";
+
+  console.log(result);
+}
+
+function moveToClosestLineBreak(start: number): Promise<number> {
+  return new Promise((resolve) => {
+    const stream = createReadStream(fileName, { start, end: start + 128 });
+    stream.on('readable', () => {
+      const chunk = stream.read(128);
+      const offset = chunk.indexOf("\n".charCodeAt(0));
+      resolve(start + offset);
+      stream.close();
+    });
+  });
+}
diff --git a/src/main/bun/J-Sek/package.json b/src/main/bun/J-Sek/package.json
new file mode 100644
index 0000000..eeefe07
--- /dev/null
+++ b/src/main/bun/J-Sek/package.json
@@ -0,0 +1,11 @@
+{
+  "name": "1brc",
+  "module": "index.ts",
+  "type": "module",
+  "devDependencies": {
+    "@types/bun": "latest"
+  },
+  "peerDependencies": {
+    "typescript": "^5.0.0"
+  }
+}
\ No newline at end of file
diff --git a/src/main/bun/J-Sek/tsconfig.json b/src/main/bun/J-Sek/tsconfig.json
new file mode 100644
index 0000000..dcd8fc5
--- /dev/null
+++ b/src/main/bun/J-Sek/tsconfig.json
@@ -0,0 +1,22 @@
+{
+  "compilerOptions": {
+    "lib": ["ESNext"],
+    "target": "ESNext",
+    "module": "ESNext",
+    "moduleDetection": "force",
+    "jsx": "react-jsx",
+    "allowJs": true,
+
+    /* Bundler mode */
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "verbatimModuleSyntax": true,
+    "noEmit": true,
+
+    /* Linting */
+    "skipLibCheck": true,
+    "strict": true,
+    "noFallthroughCasesInSwitch": true,
+    "forceConsistentCasingInFileNames": true
+  }
+}
diff --git a/src/main/bun/J-Sek/worker.ts b/src/main/bun/J-Sek/worker.ts
new file mode 100644
index 0000000..834d373
--- /dev/null
+++ b/src/main/bun/J-Sek/worker.ts
@@ -0,0 +1,72 @@
+import * as fs from 'node:fs';
+
+declare var self: Worker;
+
+const cities = new Map<string, CityValues>();
+type CityValues = { min: number; max: number; avg: number; count: number };
+
+self.onmessage = async (event: MessageEvent) => {
+  const { fileName, start, end } = event.data;
+  await readStream(
+    fs.createReadStream(fileName, { start, end }),
+    acceptLine,
+    () => {
+      postMessage(cities);
+      process.exit();
+    }
+  );
+};
+
+function acceptLine(line: string) {
+  if (line.length < 3) return; // skip empty lines
+
+  const [city, value] = line.split(";");
+  const v = Number(value);
+
+  if (!cities.has(city)) {
+    cities.set(city, { min: v, max: v, avg: v, count: 1 });
+  } else {
+    const values = cities.get(city)!;
+
+    if (values.min > v) values.min = v;
+    if (values.max < v) values.max = v;
+
+    // hack: average is not expected to change after certain number of measurements
+    if (values.count < Number.MAX_VALUE / 100) {
+      values.avg = (values.avg * values.count + v) / (values.count + 1);
+    }
+    values.count += 1;
+  }
+}
+
+async function readStream(
+  stream: fs.ReadStream,
+  accept: (line: string) => void,
+  done: () => void
+) {
+  const lineBreak = "\n".charCodeAt(0);
+  const textDecoder = new TextDecoder();
+
+  // max line length is 128
+  let lineBuffer = new Uint8Array(128);
+  let lineBufferLen = 0;
+
+  for await (const chunk of stream) {
+    for (let i = 0; i < chunk.length; i++) {
+      if (chunk[i] === lineBreak) {
+        const line = textDecoder.decode(lineBuffer.slice(0, lineBufferLen));
+        lineBufferLen = 0;
+        accept(line);
+      } else {
+        lineBuffer[lineBufferLen] = chunk[i];
+        lineBufferLen++;
+      }
+    }
+  }
+
+  if (lineBufferLen > 0) {
+    accept(textDecoder.decode(lineBuffer.slice(0, lineBufferLen)));
+  }
+
+  done();
+}