Casino operators with millions of dollars at stake in Maryland's plans to expand gambling by allowing a site in Prince George's County have ramped up spending again, giving more than $15 million to pro- and anti-casino groups as the November election draws closer.

The battle of gambling ads in the Washington and Baltimore media markets has played out much like a high-stakes poker game -- a game that will be allowed in Maryland casinos if voters approve a ballot question authorizing a sixth state casino, table games such as blackjack and roulette, and 24-hour operation.

When one gambling company raises the stakes, donating millions of campaign dollars, a competing group is there with millions of dollars more.

The Peterson Cos., developer of National Harbor -- the likely destination of a Prince George's casino if the ballot question is approved -- entered the fray last week, contributing $400,000 to the pro-casino committee For Maryland Jobs and Schools.

The company was joined by first-time contributor CBAC Gaming LLC, a collection of business groups led by Caesars Entertainment Corp. that want the authorization to include table games at a downtown Baltimore casino.

Not to be outdone, Penn National Gaming Inc. donated $4 million to anti-gambling committee Get the Facts - Vote No On 7 after news broke of the Peterson Cos.' first contribution.

Penn National, which would lose business at its casino in West Virginia if a gambling site opened in Prince George's, had given $9.5 million to the committee as of Friday, according to elections officials.

The Caesars group contributed $1.1 million, according to the latest filings with the Maryland State Board of Elections. Combined with contributions from MGM Resorts International, the group has spent $5.3 million so far.

For Maryland Jobs and Schools rolled out a new TV ad on Friday afternoon touting the jobs and business that a Prince George's casino could bring to Maryland.

Casino ads have become a mainstay of commercial breaks during local news broadcasts, prime-time television shows and Sunday afternoon football games -- between ads for the presidential election and the U.S. Senate race in Virginia, there's little time for other commercials.

"There's just no room," said Trevor Parry-Giles, a professor of political communication at the University of Maryland, College Park. "Even the mattress folks and car ads are being crowded out."