OIL and gas giant Shell announced the final terms of the plans to scrap its complex 100-year-old structure yesterday and said completion of the boardroom unification would take place by July 20.

Creation of a merged group, to be known as Royal Dutch Shell, became a priority following Shell's shock downgrading of its oil reserves last year.

Many shareholders blamed the company's two-board structure for a lack of management control at both Royal Dutch and London-based Shell Transport & Trading.

The debacle prompted a slump in the company's share price and claimed the scalps of three top executives, including chairman Sir Philip Watts.

Under the plans to create a single-parent company with "one board, one chairman and one chief executive", Shell believes it can produce benefits including increased clarity and simplicity of governance, increased management efficiency, increased accountability, and f lexibility in issuing equity and debt.

The combination remains subject to shareholder approval, and investors will get the chance to vote on the proposals at the two annual meetings next month. The UK business will hold its event in London on June 28.

Jeroen van der Veer, chief executive of Shell, said: "We have been encouraged by the widespread support of shareholders since the unification proposals were announced in October last year.

"In publishing the full documentation, we remain firmly on track for the completion of the transaction in July."

Shell also said it planned to continue the Dollars3bn to Dollars5bn ([pounds]1.6bn to [pounds]2.7bn) share buyback scheme for this year announced in February.

The firm intends to repurchase stock from Dutch shareholders in preference to those shares held by UK investors.

The decision is in line with Shell's strategy to take the most cost-effective approach to buy backs.

Royal Dutch Shell has applied for its shares to be listed and admitted to trading in London and Amsterdam.