Bicycle Mechanics - Pedals frozen on cranks

I bought a used bike on craigslist. It's in very decent shape, but tonight when I went to change the pedals, it seems the pedals are frozen on the crank arms.

I've tried some penetrating oil but nothing seems to work.

Any advice?

don't forget the left pedal is reverse threaded.
other than that; bigger hammer.

I agree with the Firebolt. Left crank, left handed threads and a bigger hammer. When you install the new ones don't overtighten them and grease the threads.

Soak the things in PB Blaster for a day. Then put a nice, long hunk of pipe on the handle of a good pedal-wrench. Now try it.

When you install new pedals, grease the threads generously. Your Future-Self will thank you!

I hope you're using a wrench like this: http://www.jensonusa.com/store/product/TL707B01-Park+Pw-3+Pedal+Wrench.aspx

Leverage is your friend, and position the wrench and crankarm so you can maximum mechanical advantage. Soaking for hours with Liquid Wrench or PB Blaster will tilt the odds in your favor.

Also brace yourself and/or wear gloves - knuckles vs chainring is not pretty.

Whacking the crank near where the pedal is helps as well. Helps break the bonds sometimes. If it's really stuck, be prepared for a new crankarm.

you can also try *carefully* heating the crank arms with a blowtorch, in addition to the penetrating oil and sharp blows.

Beware what side you are tackling and tighten it first. Sounds crazy but tightening a bolt/nut first then loosen it can work pretty good.

Is the crank on or off the bike? I've often had the best luck with the crank removed. Put an open end wrench firmly in a bench vise, stick the pedal in it, and you can really lean into the crank (wearing leather gloves). Of course, I'd start by soaking with penetrating oil and rapping the crank with a plastic mallet.

Well, I ended up taking it in this morning to my LBS and they did it in about 5 minutes. Didn't charge me either. All is good now.

Thanks everyone

how did they do it?

I find it easier to remove and install pedals with the bike turned upside down. Even with a repair stand it's difficult to hold the bike solid enough to put really good leverage on the wrench.

The bike shop put it on the stand and one of the mechanics squirted some kind of lube onto the thread.
Then he used a pedal wrench and really gave it a push. Both pedals were tightened too much and therefore froze.
The new eggbeaters were put on properly.