I'm using Selenium ChromeDriver in c# and am trying to launch multiple browser runs in parallel.

I can launch them in parallel alright but noted that they are running on multiple tabs in one browser.. can I somehow specify (in ChromeOptions perhaps) to run each test in a newly spawned browser?

This is my code :

    public void TestInParallel()
        Parallel.ForEach(scenarios, (scenario) =>
            using (var driver = new ChromeDriver(devOptions))
                foreach (var action in scenario.Acties)
                    driver.Manage().Timeouts().ImplicitWait = TimeSpan.FromSeconds(10);
  • 2
    Using multiple browser windows at the same time could give you unwanted results, for instance when using cookies, which are being shared among sessions.
    – Bouke
    Sep 7, 2018 at 13:49
  • yes, I would like to run them in incognito modus for that. (devOptions.AddArgument("--incognito");)
    – AardVark71
    Sep 7, 2018 at 13:52
  • Even in incognito mode this is not possble, because sessions will also be shared in incognito modus. You can have a maximum of two concurrent sessions, one in regular mode and one in incognito mode. I seems possible with using different user profiles though, as explained here: stackoverflow.com/questions/13301965/…
    – Bouke
    Sep 7, 2018 at 13:57
  • ouch....I couldn't believe it, but just spawned 4 incognito browsers and yes.... same sessionid is reused starting with the third browser..
    – AardVark71
    Sep 7, 2018 at 14:18
  • Couldn't believe it either when I experienced it myself.
    – Bouke
    Sep 7, 2018 at 14:20

2 Answers 2


I'm not sure how you tested your sessions issue but having two webdrivers in parallel is a normal case and there should not be issues with cookies or whatever. Below is my test written in Java but you can easily implement it in C#:

public static void main(String[] args) {
    System.setProperty("webdriver.chrome.driver", "E:/Dev/WebDrivers/chromedriver.exe");
    WebDriver driver1 = new ChromeDriver();
    WebDriver driver2 = new ChromeDriver();
    System.out.println("Driver1 cookies: " + driver1.manage().getCookies());
    System.out.println("Driver2 cookies: " + driver2.manage().getCookies());

So here you create two instances of WebDriver and each one will be operating with its own cookies set. I just checked that with amazon website since it uses sessions to track what you're doing on the site even if you're not logged in. Below is the output:

enter image description here

With this approach each webdriver opens their own window (not a tab).

  • The behavior I saw was visually.. I'm not running headless so I just see this happening. I'll do a test and print out the cookies
    – AardVark71
    Sep 7, 2018 at 15:08
  • You probably used the same webdriver instance. The idea is to instantiate two webdriver objects in memory. My example works for a regular chrome run. Not headless one.
    – Alexey R.
    Sep 7, 2018 at 15:13
  • I'm using a "using" statement.. scope of each webdriver instance should be isolated.
    – AardVark71
    Sep 7, 2018 at 15:30
  • In ChromeOptions I used each time the same remote-debugging-port. Wonder if that matters
    – AardVark71
    Sep 7, 2018 at 15:31

I've asked myself an year ago the same question that you ask here.

What I came up is using soucelab example of using ThreadLocal for storing the webdriver objects and using Selenium-Grid to consume the webdriver requests.

I've done some load/stress test with that configuration to check how stable is selenium grid and the webdriver using that ThreadLocal approach.I've modified a little bit their samples to connect to my local selenium grid. And the result was that in testing 2 sites with 1000 iterations I get 4 failed test and 3 of them was that the site was not reachable (maybe they banned me for a certain moment of time) and 1 stale element reference which I don't know were it came from (my laptop was not in the best shape while doing that). The first failing test's was after 500-th iteration. So I can say that was pretty stable.

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