NEW YORK ( TheStreet) -- After winning seats on Chesapeake Energy's ( CHK) board in June, the company's largest investor Southeastern Asset Management is adding to its bet on the embattled oil and gas driller. Southeastern Asset Management, run by Mason Hawkins, bolstered its leading stock position in Chesapeake by roughly 3.5% in the second quarter, buying up roughly 3.12 million shares, according to Securities and Exchange Commission filings compiled by Bloomberg. The share increase puts Southeastern's stake in Chesapeake Energy at nearly 90 million shares, or roughly 13.5% of the company, according to SEC filings. Southeastern's additional buying may be seen as a vote of confidence in the Oklahoma City-based driller. Hawkins, who had more at stake than any other Chesapeake investor even before his second quarter buying, argued as Chesapeake shares were dumped earlier this year that there was significant value to be realized in Chesapeake's assets. Hawkins also reclassified his firm as an activist investor at the time that Chesapeake shares bottomed out. Investors are also likely to watch whether Carl Icahn, a new Chesapeake shareholder who recently gained a board seat after taking a 7.5% stake in the company worth $1 billion, also follows suit in adding to his stock position. In late 2010, Icahn built a position in Chesapeake shares as the stock hovered in the low $20s and talked up his ability to drive change at the company, only to sell out of shares quickly after a rapid rise in value. Chesapeake shares have risen from a May low near the $13 mark -- which triggered a new round of Icahn buying -- to over $19. Icahn recently said in response to a question during a CNBC interview that even after the rebound in Chesapeake shares it was not time to sell. In Tuesday trading, Chesapeake shares rose slightly to $19.10. The stock has gained over 20% from levels that UBS analysts calculate Icahn bought Chesapeake Energy shares at in May. Year-to-date shares are off over 14% and nearly 40% in the past 12 months, amid concerns about its balance sheet, loans taken out by CEO McClendon tied to a 2.5% personal investment in wells that the company has drilled over the years, a federal investigation into allegations of price fixing in land acquisitions made by Chesapeake and rival Encana, as well as the decline in natural gas pricing to a level that remains uneconomic for many drilling companies. In June, Southeastern and Icahn's activist campaign led to a reshaping of Chesapeake's board, highlighted by the separation of co-founder Aubrey McClendon's CEO and chairman role. In the overhaul, McClendon was replaced as chairman by former ConocoPhillips ( CHK) chair Archie Dunham, but maintains his chief executive role. Chesapeake Energy also elected four other independent members to its nine-member board of directors, including three proposed by the company's largest shareholder Southeastern Asset Management and one proposed by Icahn. Those elections and Dunham's replacement of embattled CEO McClendon as chairman came as a quick response to Southeastern and Icahn's calls for drastic change that will help Chesapeake better manage its finances as a cash crunch looms. When Chesapeake announced its board overhaul, Carl Icahn said, "Chesapeake is now heading in the right direction. With the Board providing strong oversight, the management team will be sharply focused on realizing the value of its assets and the company will be well positioned to create substantial value for shareholders going forward," in a June 21 statement. Chesapeake Energy's second quarter earnings, released on Aug 6, were marked by improved forecasts surrounding the company's asset sales and reduced spending plans. The company, which is the second-largest natural gas producer in the U.S., said in June it would sell its stake in Chesapeake Midstream Partners to energy investor Global Infrastructure Partners for $4.08 billion and said in second quarter earnings it would sell some Permian Basin assets to EnerVest -- a common buyer of Chesapeake assets -- for an undisclosed price, in addition to two other Permian deals it plans to announce in the coming months.