Penn West shares dropped 3.5 per cent or 41 cents to $11.19 on the Toronto Stock Exchange after earlier falling as low as $11.05.
The Calgary-based oil and gas producer said the senior executives whose departure was effective immediately are: Hilary Foulkes, executive vice-president and chief operating officer; Thane Jensen, senior vice-president and operations engineering; James Burns, vice-president of corporate planning; and Wendy Henkelman, vice-president, treasury.
The company did not offer an explanation beyond that "improved execution is the key to realizing the value inherent in the company's asset base."
"We will continuously make the necessary changes to deliver on our business plan," it said.
The company has been restructuring, partially to pay down debt.
Penn West agreed in principle last month to sell $1.3-billion worth of its non-core properties, representing the equivalent of 12,000 barrels per day of production.
The Calgary-based company said it would use funds from the sale to repay a portion of the money drawn on its credit facilities.
"Recently announced agreements to sell assets have provided Penn West with operational and financial flexibility, allowing the company to maintain its dividend while applying capital to high rate of return projects in its portfolio," it said in a release Tuesday.
The company has been positioning itself to concentrate on light-oil plays, particularly along the Cardium formation in southern Alberta.
During the most recent third-quarter, risk management activities helped pushed the oil and gas producer into the red. Last week, it reported a net loss of $67 million or 14 cents per share in the quarter.
That compared with year-earlier net income of $138 million or 29 cents per share.
The big swing was mainly due to unrealized losses or gains on the company's risk-management contracts, partially offset by unrealized foreign exchange gains and losses.
By other measures, Penn West had a more stable quarter.
Revenue was $840 million, down from $861 million a year earlier. Funds flow was $344 million or 72 cents per share, down from $348 million or 74 cents per share. Production fell to the equivalent of 160,339 barrels of oil per day from 161,323 barrels per day.