Below is a list of common expenses for a typical Gas Station / Convenience Store Operation.  These figures are estimates and will vary depending on the location:
Payroll: 24 Hour Locations: 720 man hours per month X $8.05 per hour = $5,796.00 per month for one employee per shift. 18 Hour Locations: 540 man hours per month X $8.05 per hour = $4,347.00 per month for one employee per shift. Add 7% for payroll taxes and workman’s compensation to get an accurate total.
Utilities:  Electric, Water, Sewer, Garbage and Phone approx. $2,000.00 per month.
Insurance:  Average liability, property and tank insurance total $7,000 per year.
Credit Card Fees:  This expense is variable based on the volume of the location.  An easy way to get a close estimate is to use the following formula:  Gallons per month X Average gas price X Percentage of credit card sales X 2.5% = credit card fees. Example-  A location pumping 100,000 gallons per month at $2.50 per  gallon, doing 35% cash business and 65% credit card business will look like this: 100,000 X $2.50 X 65% X 2.5% = $4,062.50 per month.
Miscellaneous:  Accounting Fees, Bank Fees, Lawn, Pressure Washing, Maintenance etc.  $700.00 per month.