Oil and gas explorer Beach Energy Ltd (ASX: BPT) says it has increased its relevant interest in Impress Energy Ltd (ASX: ITC) to above 45 percent, as a result of continued strong on-market acceptances by Impress shareholders.

The former announced on Monday a recommended and unconditional on-market cash offer for all of the issued and outstanding shares of Impress that it does not own, for 8.5 cents per share.

Beach, through its broker Euroz Securities Ltd, has increased its relevant interest in Impress to above 45 percent through on-market buying, the company said in a statement.

Beach Managing Director, Reg Nelson, said "The certainty and fair value of our offer continues to be the main driver behind consistently strong selling by Impress shareholders.

Without another option currently available to shareholders, and with the majority of Impress Directors selling their shares, we feel it will only be a matter of time before other Impress shareholders follow suit."

The offer price represents a quarter of a cent increase on the merger proposal price under the scheme of arrangement. It also represents a 39 per cent premium to the one month volume weighted average price of 6.1 cents per share before the announcement of the proposed merger on November 22, 2010.