The prospects of a major merger between two partnerships to create one huge natural-gas pipeline system took a step forward as William Cos. improved the terms of an improved deal for the merger, according to the Wall Street Journal.

Under the terms of the deal, unveiled on Sunday, Williams Cos. would increase the incentives for investors on both sides, which was a movement forward from its offer of $6 billion to expand ownership in Access Midstream Partners, which was proposed in June. After the deal, completed in July, Williams had a 50 percent stake in Access.

Williams, a pipeline based in Oklahoma, wants to boost its involvement in using new technologies for shale drilling in order to increase production of oil and natural gas. Access Midstream focuses on wells in Texas, Pennsylvania, and Oklahoma, where it drills for the resources and then ships them to larger pipelines.

Williams Chief Executive Alan Armstrong said in a statement that it is “another big step toward” the company’s goal of being the No. 1 natural-gas infrastructure provider on the continent.

Master limited partnerships have become popular with energy companies, as they attract yield-seeking investors. Due to their tax status, they don’t have to pay corporate taxes to the federal government and can send that money to shareholders as if they were dividends.

Partnerships allow the payments to continue growing, which is what continues to make these types of partnerships attractive, and before Williams merger attempt, there have been numerous acquisitions by these partnerships recently.

Williams’ proposal would allow investors who own units of Williams to receive 0.87 units of Access for each Williams unit they own — more than what the original proposal stipulated.