Q:

Should I continue studying OpenGL or just switch to DirectX to  give me a better chance of landing a job in the game industry?

I've been learning graphics programming for some time now using OpenGL and Linux. I'm pretty familiar with most of the concepts, but I would really like to further my knowledge and eventually pursue a career in game development, especially game engine development.
So far it seems to me that the majority of game studios make games for Windows using DirectX. 
Edit: I know that the OpenGL vs DirectX question has been asked here before, but I haven't found an answer in the perspective I want.
Edit 2: After reading all the responses/comments I've decided to continue diving deeper into graphics with OpenGL/GLSL, but I'll try to play around with DX as well, just to have a basic understanding of the API. 
I'd like to thank everyone for the answers and insight you've given me.

A:

It really doesn't matter.  The core concepts are the same in both, especially now that pixel shaders are the norm. And since most games are multiplatform they're probably going to use a subset of features that are similar in both languages.  As long as you can write shaders in glsl or hlsl, you'll be fine.
That being said, the number of "game engine development" positions out there are small.  Most companies use something off the shelf.  For those positions that exist, even fewer of them are entry level.  Most entry level game programmers don't write any graphics-related code (other than maybe shaders) because it's all been abstracted away.

A:

It all depends on the job you want/will get. You probably think about a job in the PC market where DX is king. Just remember that most AAA companies aim for the console market where APIs are quite specific.
The PS3 for example has proprietary extensions to its OpenGL ES implementation.
OpenGL is growing in the mobile space. Now it's available on all modern platforms but Windows Phone 7.
Currently Only OpenGL ES is available in this space. But more Powerful PowerVR chips are coming with support for OpenGL 4 and DX11.
Your OpenGL skills are gold. You can reconvert to DX to land a job which requires that. But in the meantime remember that OpenGL is king on the quantity of devices and platforms where it is available.

Edit: Additionally more and more companies tend to use existing engines and often even core game developers are more and more screened from the low level APIs. It's always better to have a good knowledge of native APIs when you are facing bugs and strange behavior on specific platforms. But it all comes down to the concepts, and as others pointed out DX and OpenGL at the core will require knowledge of the same concepts.

Edit: As you are already familiar with OpenGL and probably shaders you should try OpenCL... This API has the potential of becoming the next big thing in parallel computing.
I'm mentioning it as the OpenCL kernels use datatype that are interoperable with OpenGL and are simple to understand for OpenGL devs. Have a look at that and see if you can acquire some experience with a great general computing solution (currently being integrated into bullet physics for example).

A:

I agree, that it doesn't really matter which API you learn. It's important to know the basic concepts.
When looking at game development, Windows is not the only target platform. As I've heard, Apple is growing as a target platform, but the consoles are really important as well. Consoles normally have their own specialized graphics API (I think they're doing that just to bother us). While the console APIs tend to have more in common with OpenGL than with DirectX, it's still not a huge difference.
Go with whatever works for you.

