Some women find it incredibly difficult to achieve orgasm from penetration alone and need clitoral stimulation - and there is nothing wrong with that. There is no set of rules that says a woman "should" be able to orgasm from either. Generally, more women do find it easier to achieve an orgasm if they incorporate some form of clitoral stimulation into their sex life. And there is a very good reason for this - the clitoris is the most sensitive part of a woman's body and was designed to create pleasure. Certainly, there is the possibilty of achieving an orgasm solely from vaginal penetration through stimulation of the G-Spot - naturally, this takes time, patience and practice, but there are plenty of helpful resources online that can explain these methods to you in more detail. There is nothing wrong with not being able to achieve an orgasm from penetration alone, and it in no way reflects badly upon yourself or your partner. Everyone is different - the important part is that you discover methods that work for you both, and that you are both comfortable with what is happening. If you are concerned with your inability to achieve an orgasm from penetration, you can certainly consult with a Gynocologist or your GP for further information.

For 25% of women, it never happens at all. It may be that you are part of that 25%. For another 50%, it can happen occasionally or rarely, perhaps with additional clitoral stimulation at the same time. I can orgasm in modified missionary with my legs down and together. But it is incredibly rare, very hard work and just too much hassle. Most of the friends I've actually discussed this with are the same. One said it was very rare for her and too much like hard work, another that she couldn't orgasm at all without a vibrator, and a third had just had her first orgasm during intercourse at the age of 37. So I wouldn't worry :-) If you really want to, try some of the positions that are supposed to help, such as the Coital Alignment Technique etc. There are quite a few positions you can look up on the web. Or try getting your partner to bring you right to the edge of orgasm before he penetrates you. The great thing about the CAT, which is the modified, legs-straight missionary I mentioned, is that the whole length of his peni stimulates your clit as he thrusts. You might find that helps.