Using PS CS 6 how to make an oval gradient

I just want to make a gradient, transparent to black, like a vignette only more so, on an image that is four times as wide as high. I can make a circular gradient, and start it at the centre using the ALT key, but I can't make it oval. I'm using PS CS 6, Win 7x64.

I know this is simple, I even used to know how to do it, but the brain isn't responding. Can someone tell me what I'm missing?

David