Tullow Oil says interim revenue will likely fall 23% following a drop in production and lower commodity prices.Revenue for the interim period is put at about £290m, down from £378m in 2008 when oil was trading near $150 a barrel. It's closer to $60 today.It expects annual production to average 58,000 barrels of oil equivalent per day (boepd) following a 16% drop in output during the first half.The company produced 59,000 barrels a day in the first six months of 2009, lower than last year's equivalent due to mixed results from infill wells in the UK, partly offset by higher production in Africa. Expect capital expenditure to leap from £700m for 2009 as a whole after £425m was spent in the first half.Development of the Jubilee field in Ghana remains on track for first oil in the second half of 2010."The outlook for Tullow remains very positive," said chief executive Aidan Heavey.Results for the half-year ended 30 June 2009 are due on 26 August .