NEW YORK (Bloomberg) – Pride International Inc., the US oil and gas driller with rigs from India to Africa, said its board lowered the threshold to trigger a rights plan to 10 percent from 15 percent after Seadrill Ltd. acquired a stake. Pride shares had their biggest gain in almost two years.

Pride was notified that Norway's Seadrill acquired about 9.9 percent of the company's outstanding stock, the Houston-based company said yesterday in a statement. Pride spokesman Jeffrey Chastain said in an interview Seadrill has not provided information about its intentions, plans or proposals.

"They're saying if you're not going to talk then we're going to make sure you can't do anything," Roger Read, an analyst at Natixis Bleichroeder, who rates Pride shares at "buy" and doesn't own any, said in an interview.

Seadrill, a Bermuda-based oil-rig company run from Norway, said in November 2006 it may be looking to take over a US oil-rig competitor. The company, set up by billionaire John Fredriksen, also has been seeking to raise as much as $6.4 billion in equity for acquisitions.

Seadrill chief operating officer Alf Thorkildsen said yesterday in a telephone interview the stake in Pride was a "financial investment," and declined further comment.

The stake makes Seadrill Pride's largest single shareholder.

Pride gained 6.1 percent to $42.88 in New York Stock Exchange composite trading, after earlier touching $43.45. It was the largest one-day gain since June 15, 2006. Seadrill rose four percent to 156 kroner in Oslo.

"If the share price (of Pride) doesn't go up too much, they (Seadrill) might be interested in buying parts of the company, but Pride's fleet, because it has a lot of jack-up rigs and is older, is not that interesting for Seadrill," said Stian Eliassen, an analyst at Carnegie ASA in Oslo, who has a "neutral" rating on Seadrill stock.

Jack-up rigs have retractable legs that extend to the seafloor and are the most common type used for shallow-water drilling.

Pride operates 62 rigs in the Gulf of Mexico, South America, Africa and India, according to the company's website. It also has three deepwater drillships under construction for delivery in 2010 and 2011 at a cost of $2 billion.

Seadrill's drilling fleet is one of the most modern because of its focus on technically demanding segments of the offshore drilling industry, such as deepwater and harsh- environment rigs, according to its website.

Seadrill is the world's sixth-largest offshore oil driller with 38 drilling units, of which 12 are under construction.

Seadrill has a reputation for making such financial transactions and then selling them later for a gain.

The company in March booked a $6 million gain from the sale of a stake in Odfjell Invest Ltd., a supplier of harsh environment deepwater semi-submersible drilling services.

The Nordic company has bought stakes in other competitors, including Aker Drilling ASA and Scorpion Offshore Ltd.

Pride's management is "reasonable" and would negotiate a sale, said Mr. Read of Natixis Bleichroeder.

"If it goes hostile though, they'll clearly ask for a higher price," he said.