Woodside Petroleum Ltd. is expanding its push into West Africa, agreeing to buy ConocoPhillips' (NYSE: COP) deepwater stakes off Senegal, including one of the world's most promising recent oil finds, for up to $430 million.

The move brings a deepwater expert into the SNE Field off Senegal and removes uncertainty over its ownership, which may help speed up development of a billion barrel resource that is expected to start producing within the next five years.

Australia's FAR Ltd. owns 15% of the fields and Senegal's state-owned Petrosen holds 10%.

FAR Ltd. Managing Director Cath Norman could not be reached for comment on July 14, but told reporters on July 13 that the SNE Field could start producing as early as 2019 if plans go ahead for a floating production operation.

FAR's shares fell as much as 20% on the Woodside announcement, then rebounded slightly to end down 10.7% at A$0.075, valuing it roughly in line with the price Woodside agreed to pay for ConocoPhillips' Senegal stake. Woodside shares fell 1%.

The acquisition includes a 35% interest in the 560 million barrel SNE deepwater oil discovery and the FAN oil discovery further offshore, with Woodside gaining the option to become operator for development and production of the fields, for what one analyst said was a cheap price.

"We are taking advantage of our balance sheet to acquire a world-class asset that fits well with our capabilities, offers significant future upside in exploration and line-of-sight to near term oil production," Woodside CEO Peter Coleman said in a statement.

The deal, for $350 million plus payments of up to $80 million, is key for cashed-up Woodside, as it is short of growth prospects after scrapping multi-billion dollar plans to develop gas off Israel, postponing plans to develop the Browse gas project off Australia and being spurned in a takeover offer for Oil Search Ltd.

"We see the deal pricing as an attractive entry point for Woodside given that the 560 million barrels-plus is relatively well appraised," RBC analyst Ben Wilson said in a note.

Woodside has already targeted the area off Senegal for exploration, with a stake in the AGC Profond block in a zone between Senegal and Guinea Bissau.

ConocoPhillips flagged last year that it was looking to sell its deepwater exploration stakes and said July 14 the sale of the Senegal holding was an "important milestone."

The fields' operator is currently Britain's Cairn Energy Plc, which owns 40% and is looking to sell down its stake to cut its funding obligation for exploration and appraisal.

Cairn shares fell by more than 4% by 4:25 a.m. CT (9:25 GMT) as the implied value of its Senegal asset took a material hit following the deal announcement, according to Jefferies analyst.

The "only way to sugar coat this is to see a clean exit/entry for cash with a reputable deepwater operator," Jefferies said.