U.S. President Barack Obama, a fierce advocate for gun regulation, is an unlikely investor in the firearms industry — yet he has money in a pension fund that holds stock in gun and ammunition companies.

Although Obama's stake is minuscule, worth no more than $30, it reflects a much larger surge of investment.

The president is among millions of Americans investing in gun companies — often unwittingly — as mutual funds have increased such holdings to record levels, according to a Reuters analysis of institutional investment in firearms companies.