The New York-listed tanker owner said quarterly dividend will rise to $0.4375 per share from $0.3125 per share. The increase results in an indicated annual rate of $1.75 per share.
"These actions are possible due to our strong operating results and reflect our confidence in the ability of our businesses to generate strong levels of cash flow into the future," Morten Arntzen, president and CEO of OSG, said in a statement.
"This also demonstrates our commitment to capital discipline and shareholder value creation. We believe that this decision by our Board strikes a good balance between maintaining the necessary balance sheet strength and financial flexibility to grow our businesses and return value to our shareholders."
The new $250 million share buyback programme replaces the prior $200 million share buyback programme that was completed during the second quarter of 2008.
In May, OSG bought back 280,000 shares at an average price of $77.48. Over the past year, the company has repurchased 9.3 million shares at an average price of $66.25 a share, or 23.43% of total shares outstanding, at a total cost of $614 million.
OSG said it expected to repurchase more shares from the open market, "at times and prices that are considered to be appropriate by the Company".
The August dividend of $0.4375 per share will be payable on August 27, 2008 to shareholders of record on August 6, 2008.
OSG reported a net profit of $112.4 million in the first quarter ended March 31, 2008, up from $84.7 million a year ago.