You usually have enough fuel to reach your patrol point, spend a good amount of time there and make it back to base OK. You'll want to have modded keys or buttons to Max Range at Current Speed and Range to Course End, so you can easily check if you have enough gas to get back home.
All of that is assuming that you're cruising at standard speed and not flank or full. You can also burn up a lot more fuel being decks awash a lot or by using high speeds during intercepts.
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