Indiana Treasurer Richard Mourdock drove his state-owned vehicle more for personal matters than official business until federal campaign finance rules recently prompted him to largely stop using it, a newspaper reported Sunday.

The Journal Gazette of Fort Wayne said Mourdock has driven 21,305 personal miles since July 2010 compared with 8,003 for business.

Mourdock has virtually stopped using his state car in recent months because of complicated federal campaign finance rules, spokesman Ian Slatter said. Mourdock is running for the Republican nomination for U.S. Senate next year.

"There are nuances in federal election campaign law, which are not present in state election law, regarding the use of state assigned vehicles," he said. "Rather than risk any question that the vehicle has been used for any purpose which may be considered 'campaign related,' Treasurer Mourdock has opted to not use the vehicle."

The newspaper's report examined the use of state-owned vehicles by state employees including elected officials. It said Mourdock, Auditor Tim Berry, Attorney General Greg Zoeller and Superintendent of Public Instruction Tony Bennett all use take-home cars, logging business and personal miles and paying taxes on the latter benefit.

Bennett and Zoeller logged more than 42,000 total miles in the past year and Berry drove about 37,000. Zoeller had the fewest personal miles with 6,227. Berry drove 22,827 personal miles and Bennett about 14,000, the report said.

Gov. Mitch Daniels doesn't use a state-owned motor vehicle because he is always escorted by state police. Lt. Gov. Becky Skillman used one vehicle during some of her term but does not currently. Secretary of State Charlie White has no take-home car assigned to him.

The state's vehicle management policy for most state employees allows only "de minimis personal travel," or something that is so minimal as to have no real effect, such as stopping at the grocery along one's normal route home.

Elected officials aren't bound by that rule.

"They are encouraged to adopt the same policies, but it's up to their discretion," said Tony Green, general counsel for the Indiana Department of Administration.