KANSAS CITY, Mo. -- Gov. Jay Nixon is promising Missourians "tens of thousands" of new jobs, thanks to a new law expanding tax breaks to businesses.

Nixon flew around the state Thursday to celebrate the signing of a bill that eliminates Missouri's corporate franchise tax for most of the businesses that pay it. It also increases the tax incentives available for employers who expand their payrolls or plants.

After signing the bill in Jefferson City, Nixon took out for stops in St. Louis, Columbia and Kansas City, promoting the bill as tactic against the state's soaring unemployment rate. Missouri's unemployment rate was 8.1 in April, the most recent month for which figures are available, down from a 25-year high of 8.7 percent in March.

Speaking at the headquarters of architectural and engineering firm HNTB Corp. in Kansas City, Nixon said the bill, which passed on the session's final day, capped a session in which job creation had become the top priority for Nixon and some Republican legislative leaders.

"You are never really happy as a governor when someone wants a job and can't have one," Nixon said. "We are working hard every day to make sure people get back to work."

But the bill passed only after supporters of expanded business incentives compromised with lawmakers who fear tax credits are draining the state's budget. The final version includes new limits on tax credits for the renovation of historic buildings and for projects backed by the Missouri Development Finance Board.

The exact cost or benefit of the legislation is unclear; a legislative oversight office had not completed a financial estimate of the measure by Thursday.

Nixon also highlighted a portion of the legislation that increases eligibility for state job-training incentives.

The bill will increase the asset threshold that triggers Missouri's franchise tax to $10 million from the current $1 million. Nixon has said that will exempt about three-quarters of the roughly 20,000 businesses that currently pay the tax, resulting in a $14.5 million tax cut for small businesses.

Nixon said he's hopeful the bill will create an "even playing field" with other states by allowing new types of companies to come to Missouri. He also hopes existing companies -- such as St. Louis-based seed-maker Monsanto Co. and Lee's Summit-based battery-maker Kokam America Inc. -- will be encouraged to expand instead of leaving the state.

The law expands several popular tax credits, including the Quality Jobs program that applies to employers who add jobs with at least average wages and health benefits. The law raises the cap on Quality Jobs tax credits to $80 million from the current $60 million, giving state economic development officials greater flexibility to target businesses.

The tax credit cap will be raised to $25 million from the current $15 million for both the New Markets program and the Business Use Incentives for Large-Scale Development program.

The New Markets program provides tax credits to equity investments in development projects located in areas with significant poverty rates or low incomes. The BUILD program provides aid for companies to pay off bonds used to build their plants.

But fewer developers may be able to participate in a state program that provides a tax credit equal to 25 percent of the cost of redeveloping historic buildings. The renovation program has functioned as an entitlement for those who qualify. Through the first three quarters of Missouri's 2009 fiscal year, the state had redeemed more than $157 million of historic preservation tax credits.

The new law limits the state to approving $140 million annually in historic preservation tax credits for large projects. Renovations costing less than $1.1 million will not be subject to the cap -- an exception insisted upon by the program's advocates.

The law also limits the amount of infrastructure tax credits that can be authorized by the Missouri Development Finance Board to $10 million annually, or $25 million if three executive branch officials approve of the higher figure. Previously, the board could issue an unlimited amount of tax credits so long as the executive officials gave their approval.