Comcast Corp.'s NBCUniversal agreed to buy the 50 percent stake in two Universal Studios theme parks it doesn't already own from the private-equity firm Blackstone Group L.P. for about $1 billion.

The transaction puts the overall value of the Orlando, Fla., parks at about $3.17 billion, Philadelphia-based Comcast said in a statement Monday.

Blackstone, based in New York, paid about $275 million for its stake in 2000.

Blackstone had set a June 12 deadline for NBCUniversal to buy its stake, after which the private-equity firm would have had 270 days to sell the entire operation.

The parks comprise Universal Studios Florida, Universal's Islands of Adventure, and the CityWalk dining, retail, and entertainment area.

Comcast, the largest U.S. cable TV provider, gained majority control of NBCUniversal in January from General Electric Co. by paying $6.5 billion in cash and contributing $7.25 billion in assets to a joint venture that owns the media company.

Steve Burke, the chief executive officer of NBCUniversal, said in a statement: "The acquisition consolidates our ownership and confirms our long-term commitment to Universal Orlando and the theme park business. Universal Orlando . . . is performing extremely well."

Blackstone - which was created in 1985 by Stephen Schwarzman and Peter G. Peterson - has other entertainment-related investments such as Merlin Entertainment Group, operator of the London Eye, and SeaWorld Parks & Entertainment.

Private-equity firms pool money from investors to buy companies and then typically spend a number of years seeking to boost sales and cut costs to sell them later at a profit.

The sale price would give Blackstone and its backers a return in excess of three times its original investment.