A looming increase in the capital-gains tax rate next year is fueling sales of some privately-held businesses.

Many business owners—mostly founders who could gain a lot from a sale—are looking to close deals before next year, when the maximum tax on investment income is scheduled to rise from 15% currently to at least 23.8% on most capital gains, at least for higher-income households. Many sellers intend to convert their equity into retirement funds or just start anew.

"It just made more sense for me to take my chips off the table and go do something else," said Bert Wolf, 60 years old, who has an agreement to sell his compressed-gas business, Acetylene Oxygen Co. of Harlingen, Tex., before year-end.

Mr. Wolf added that if he waited until after the tax increase to sell, he would have to expand the business at the current rate "for at least 3 or 4 more years to achieve the same after-tax sales dollar." He is profiting on the sale of his business to Praxair Inc., a public company.

"There's a kind of a panic on to get things done," said Beatrice Mitchell, co-founder of Sperry, Mitchell & Co. Inc., a New York investment bank that is advising Mr. Wolf on the sale.