How can I open a link in new tab (and not new window)? [duplicate]

I have an 'Open' button that 'calculates' a link that should be opened in a new tab. I try to use:

window.open(url, '_blank');

But that opens a new window.

I also tried the following method:

<form id="oform" name="oform" action="" method="post" target="_blank">
</form>

...

document.getElementById("oform").action = url;
document.getElementById("oform").submit();

Still, a new window is opened, instead of a new tab.

When using simple <a href...> with target='blank', the link is opened in a new tab.

Is there a solution?

Update [2019] Most browsers today open in a new tab when you set the target to _blank. The days of popup windows is long gone. We can now use:

 <a href="some url" target="_blank">content of the anchor</a>

Most sane browsers will open the new window in a new tab.

CSS3 supports "open in new tab", by the property target-new

target-new: window | tab | none;

Update [2016]: this method never made it into the CSS3 spec, as one of the comments indicates. This shouldn't be used. However, it can be seen that most modern browsers open target='_blank' links in a new tab anyway, unless one attempts to resize the new tab immediately thereafter. However, there does not appear to be a mechanism to force this behavior in the specifications.

[2011] For a method of forcing opening in a new tab that is well supported, try the following:

<a href="some url" target="_newtab">content of the anchor</a>

Else, use this method to resize window immediately, to ensure that popup blockers do not kill your popup

Other than the CSS3 target-new option @anirudh4444 mentioned, you can't and mostly importantly probably shouldn't. You are trying to control the user's experience, when this should most likely be left up to the user.