Conoco and Philips Petroleum will fire an undisclosed number of workers in three cities after they merge later this year to form the third-largest US oil company. Jobs will be trimmed in Houston, the combined company's headquarters, and in Tempe, Arizona, and Ponca City, Oklahoma, Conoco and Phillips said in a statement. Most of the cuts will be by the end of 2003. Conoco spokeswoman Sondra Fowler declined to provide other details. Conoco, which is currently the third largest American oil group, and Phillips, the fifth largest, expect to save $750 million a year from the merger, expected to close as early as the third quarter. They agreed to combine in November in a transaction now valued at $27.6 billion. The deal still needs approval by the US Federal Trade Commission approval. ConocoPhillips' exploration and production and refining and marketing units will be in Houston, Conoco's current headquarters. Technology, financial services, human resources and some research and development will be in Bartlesville, Oklahoma, Phillips' headquarters. Jobs will not be affected there, the statement said.