According to several major surveys, only 25 percent of women always climax during sex with a partner. The rest of us either hit – or miss – depending on the night, or never orgasm during intercourse at all. Compared to the male version (more than 90 percent of men climax 100 percent of the time), the female "O" is a fleeting phenomenon.

We have the answers to help you help you hit your peak more often.

What Happens When You Hit the Big O?

When in the throes of an orgasm, it's unlikely that you could track all the subtle changes that are happening in your body. Luckily, famous sex researchers William Masters and Virginia Johnson have done it for you in their seminal work, Human Sexuality. Here's what they found…

That warm, sexy rush you feel during foreplay is the result of blood heading straight to your vagina and clitoris. Around this time, the walls of the vagina start to secrete beads of lubrication that eventually get bigger and flow together.

As you become more turned on, blood continues to flood the pelvic area, breathing speeds up, heart rate increases, nipples become erect, and the lower part of the vagina narrows in order to grip the penis while the upper part expands to give it someplace to go.

If all goes well (i.e., the phone doesn't ring and your partner knows what he's doing), an incredible amount of nerve and muscle tension builds up in the genitals, pelvis, buttocks, and thighs – until your body involuntarily releases it all at once in a series of intensely pleasurable waves, aka your orgasm.

The big bang is the moment when the uterus, vagina, and anus contract simultaneously at 0.8-second intervals. A small orgasm may consist of three to five contractions; a biggie, 10 to 15.

Many women report feeling different kinds of orgasms – clitoral, vaginal, and many combinations of the two.

According to Beverly Whipple, co-author of The G-Spot and Other Discoveries About Human Sexuality, the reason may simply be that different parts of the vagina were stimulated more than others, and so have more tension to release. Also, muscles in other parts of the body may contract involuntarily – hence the clenched toes and goofy faces. As for the brain, a recent small-scale study at the Netherlands' University of Groningen found that areas involving fear and emotion are actually deactivated during orgasm (not so if you fake it).

After the peak of pleasure, the body usually slides into a state of satisfied relaxation – but not always. "Like their male counterparts, women can experience pelvic heaviness and aching if they do not reach orgasm," says Ian Kerner, a certified sex therapist and author of She Comes First: The Thinking Man's Guide to Pleasuring a Woman.

In fact, Dr Kerner says, "many women complain that a single orgasm isn't enough to relieve the buildup of sexual tension," which can leave us with our own "blue balls." Don't worry: Like the male version, it's harmless.

The Big O Blockers

So what goes wrong on those nights when the fuse gets lit but the bomb never explodes? "Nine times out of 10 it's because (the woman isn't) getting enough continuous clitoral stimulation," Dr Kerner says.

Often, "A woman will get close to orgasm, her partner picks up on it, and (then he either) orgasms immediately or changes what he was doing."

That's why Dr Kerner frequently recommends the woman-on-top position. Because you control the angle and speed of the thrusts (try a back-and-forth motion so that your clitoris rubs against your partner's abdomen), it allows for the most constant clitoral stimulation.

Another solution is to find a position that mimics how you masturbate. If you have solo sex by lying on your belly and rubbing your clitoris with your hands tucked beneath you, then your man can enter you from behind in that position. By watching you he'll also get a better sense of the stimulation you need.

"Spectatoring" is another problem that can trip women up. "It's when a woman is too concerned with her appearance and/or performance to actually enjoy herself," Dr Kerner says. There's no way you're going to have an orgasm if you're fretting about your cellulite or stressing over whether your newest as-seen-on-late-night-cable moves feel good for him. Instead, you have to let the erotic sensations register in your mind. Focus. Breathe. Let go. "It may seem counterintuitive," he says, "but you need to relax to build sexual tension."

The best preparation for a big orgasm is probably a long, steamy shower, full-body massages by and for your man – or 10 minutes of steady oral sex, if you can get it. It's not so much your body that needs the R&R as your mind.

"Many women need a transition period between dealing with the stress of everyday life and feeling sexual," Dr Kerner says. "A few minutes of foreplay usually isn't enough." Doing something ritualistic and soothing that will clear your head of to-do lists, work issues, family problems, and whatever else might be distracting you from connecting with your body is essential to feeling ecstatic.

A Hormone Worth Getting Excited About

The most fascinating orgasmic side effect of all happens in the brain. During the big moment, the hypothalamus releases extra oxytocin into your system. Called the "cuddle hormone," oxytocin has been correlated with the urge to bond, be affectionate, and protect (new moms are drunk on the stuff).

Since an increase in oxytocin has been shown to strengthen the uterine contractions that transport sperm to the egg, those findings are giving evolutionary biologists new hope. According to Dr Lloyd, it's conceivable that the additional oxytocin gives enough of a boost to contractions that orgasm could play a part in conception after all. "Of all the avenues of orgasm research, I think the oxytocin avenue is the most promising," she says. It's even been hypothesized that having an orgasm and releasing that tide of oxytocin is a woman's subconscious way of approving of her partner as a potential dad.

The latest news is that this cuddle hormone might also be linked to our ability to trust. In a recent study at the University of Zurich, scientists asked 178 male college students to play an investment game with a partner they'd never met. Half of the students used an oxytocin nasal spray (not yet available in the United States) beforehand; half used a placebo. Those with the spray containing oxytocin were more than twice as likely to feel comfortable giving all of their money to their anonymous (but legitimate) partner. If oxytocin can help women feel more at ease about letting go and intensify orgasmic contractions, we might all want a bottle of the stuff stashed in our bedside drawers someday soon.