How do I convince my girlfriend to give me a blowjob?

Sorry, but you can't.
All you can do is make it clear you'd find it really hot/sexy if she did, and try to be understanding of the reasons she might not want to. In the end, it is her decision whether or not she will do this. That said, assuming you keep yourself clean, I think it might be worth your time to figure out why she doesn't want to, because maybe it will help you and her work through her not wanting to, change her mind and get you blow jobs.
Is it because she doesn't know how to do it? Is it because she is scared of swallowing? Is it because of she thinks it is a trashy thing to do? Did she have a bad expereince? If the two of you can be open about her reasons for being scared/disgusted etc, you might be able to explain away these reasons. Ex. If she doesn't want to swallow, letting her finish with her hand or telling her you'd still appreciate her giving you a blowjob even if she doesn't swallow might help. If she doesn't know what she's doing, (i personally think she needs to take the initiative and do some research) but maybe just your being aware of the fact she is learning might help (sexy lesson time! ). If she's up for watching porn, go for it. Also you could just see if she can slowly incorporate a little bit of tongue/mouth action into her blowjob (your appreciation might motivate her to try more) will make her gradually more confident.
Seriously, I rather give bj than hj that is a personal preference, but I give hj too. So preferences you might not be able to change, but getting her comfortable with bjs might be a possibility. Start by communicating that you like them and finding out why she doesn't. You can't pressure her into it, but it is possible a little bit of conversation/(re)education might go a long way. Also worthwhile is figuring out where both of you stand concerning you going down on her. Because she might have phobias about that and that might be her reason for avoiding oral on you, or she might feel like you want a bj but aren't ready to reciprocate. Talk to her and find out about it. Just stay positive!
Oh and this is a random afterthought because I don't want to make any assumptions about your relationship, but a bj is a lot more intimate than a hj and for some girls maybe more intimate than sex. So her not giving you bj might have to do with the stage of your relationship or whether or not you've both been tested for stds!

Lmfaoo well I'm another one of you girlfriend. I prefer hj more then bj. The only way you can most likely make her do something like that is getting her in the mood and not forcing her too. I mean like when your told to do something or asked way to many times its a turn off for a chick well in my opinion because it makes em not wanna do it anymore. Start off with dry sex let her be which ever part she likes better top or bottom. Maybe talk of your top make off her top maybe unhook her bra, massage her. Kiss her unbutton your pants jeans or just put the pants down soo you see your boxers. Maybe start rubbing her in sensitive places. Shell probably start off with giving you a hj. N then move in with playing with it with her tongue and moving into a bj. N DONT push her down to start never ever. The girl knows what she's doing trust me and your love it.

P. S I think the only reason why she doesn't wanna give you a bj is if you squirt in her mouth maybe if she does start giving you bj try not too.

Good luck
signed:its-SHORTshit

I wish you would have given more details about her blow job hang ups, it would be easier to help you. Although, I'm sure you've tried asking the basic, "Please babe, it feels so good, do it for me?" and other than that there's not much else you can do. If her issue is not knowing what to do, try reading a few blow job technique articles online together to make her feel comfortable. If her issue is with taste or the idea just seems gross to her, assure her that you won't ejaculate anywhere uncomfortable to her. Tell her that you would greatly appreciate it if she tried, and let her know that if at any point she is uncomfortable she can stop. But I wouldn't pressure her too much, that may cause a little resentment towards you on her end. You can only suggest up until a certain point but keep in mind and respect her feelings on the subject, and never force her to anything she isn't comfortable with.

Good Luck
Mango =]

If she doesn't want to, she isn't going to. Don't force her. Remember, she isn't a porn star, and probably doesn't want to get any of your "man seed" in her mouth. The majority of girls just think that's nasty, and I don't blame them.

As far as convincing her, you can't. All you can do is nicely tell her that you would love it if she would do it for you. Then maybe one day she will offer to give one, eventually.

It really is up to your girlfriend if she wants to give you a bj or not. Just like other things in life, you can't force it upon her. If it really means a lot to you and you're wanting it badly, put in some effort to get her into the mood. If you just want it out of a whim or just a quickie type of thing, I'm just going to have to say, "that's just too bad. " If there is more to this than just your girlfriend not liking it rather than not knowing how or being ashamed, like the anonymous user said she can read up on these things.

How long have you been seeing this girl?

Give her time. If she doesn't want to, then that's her decision. Why makes someone do something they don't want to do?