If the church owns a vehicle and allows the minister to use it for personal use, then it's generally best to have the church pay 100% of all expenses (including fuel) and to consider personal use as additional taxable compensation. In accordance with Internal Revenue Code Section 61(a)(1), vehicles used primary for business purposes, but occasionally for personal purposes by employees qualify for use of the standard mileage rate for taxation. For example, the minister records 1,500 miles of business use in August 2008, but 200 of personal use. Under the current $.585 standard mileage rate, $117.00 should be added to the minister's taxable earnings for August.
2008 IRS Publication 15-B provides a succinct explanation on page 20. A link is provided here:
IRS Publication 15-B