There are four considerations in using a fountain pen:
1. Weight/Balance
2. Nib/Line Size
3. Ink Flow and Nib Feel
4. Ink Drying Time
WEIGHT/BALANCE:
One of the marks of a quality pen is that it is both lightweight and balanced toward the nib end. In this way you don't have to keep a tight grip on a heavy pen, and the balance lets the weight of the pen do the writing. You don't need to press a fountain pen into the page like you do with a ballpoint. Someone else mentioned a gel pen, but this is better known in the pen world as "rollerball" because it employs a slightly improved version of the ballpoint design. That said, a rollerball (such as the G2) may be a good option for you, but you are still holding it to the page in a different way than a fountain pen in order to "get the ball rolling" (no pun intended).
NIB/LINE:
There are as many kinds of nibs and line widths as you can imagine in the world of fountain pens. Since you'll be writing a long exam, it's important to have a nib that is neat and tidy, and will be able to help you fit more words per line. If you go with an American or European fountain pen, you'll want to choose an extra-fine nib or perhaps a fine. There are many varieties of steel, platinum plated, gold, and gold plated nibs but most modern nibs offer a more rigid feel (as opposed to the flexible or springy nibs of the early 20th century) so you can't go wrong with any material as long as it's a good line width and feels right on the page.
NIB FEEL:
A nib can feel scratchy on the page if it's of inferior quality, so if you have a chance to try before you buy that's the best thing to do. If not, then stick to known brands. Since we're talking about thin lines for writing a long exam, and presumably a conservative budget, my recommendation is to look at Lamy. I currently use a Lamy Safari EF and it writes very smoothly. It's not the best balance, but if I write without the cap (i.e. unposted) it's okay. The line is a bit thicker than, say, Pilot or Sailor nibs (Japanese brands) but within my specs for school notes and tests. The Safari will set you back about $30-40 USD.
INK:
I recommend getting a converter with your pen so you can use bottled ink. Why? Because you need to use better ink than is made available in those nasty disposable cartridges. If you get the Lamy Safari, the converter is only $5. A bottle of ink is only about $8-15 and should last you a long time. I use Diamine's Midnight Blue, but it has a medium drying time (maybe 9-12 seconds) comparable to a Pilot G2. For how much you have to write, you may want to reduce smudging by using Parker Quink (drying in about 6-9 seconds). Quink also happens to be one of the more economical inks on the market.
I would strongly encourage you to do your hand a favor and switch to a fountain pen as you prepare for this exam, and start training yourself not to press the pen but actually just write with it. Also, stop by the forum fountainpennetwork.com for more info about fountain pens. They've got a lot of great information posted if you need help.
