[Zanthis]

You out run him. If he is faster than you, you ain't retreating. If you are both tied, the best you can do is keep the range unchanged.

Since you can travel through warp points in combat, their are really only two ways to get away:

1) Retreat to a warp point and warp to another system. He can of course follow, but hopefully not. If it is your system you warp to, he might fear what defenses you have waiting and opt not to follow.

2) Either he doesn't feel like chasing you (yeah right) or there is another threat greater than you in the system. If you came through a WP and ran past his WP defenses, he probably won't pull his WP defenses away from the WP to chase you down. Of course, he might have a second fleet for just such an emergency.

If you happen to have the same speed ships as your enemy, a prolonged retreat (Lasting weeks of game time) could cause your tactical engines to fail. Of course, it could also cause his to fail. All in all, you'll slowly have ships start to fall behind and get eaten if you try and retreat for weeks at a time.

I've ignored different engine techs and engine detuning, which, all things being equal, don't have a huge impact on retreating.