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Fuel leaks are generally easy to determine. First you will want to check for any fuel smells around the vehicle. Generally they will be more noticeable when the vehicle is warm and the outside temperature is hot. Check around the car or park it in a garage and come back after a few minutes to check for fuel smell.
If the check engine light is on, it could be related to a small fuel tank leak (for later model cars- 1996 and on generally). That can easily be checked by a mechanics shop with a scan tool.
Since it is a safety issue, if you question the leak at all I would have the car checked to be sure. It is easy for a shop to do a fuel system inspection, especially if they are already doing an oil change.
Please let me know if I can assist any further.