JPMorgan Cazenove has downgraded its rating for BP and slashed its target prices for the oil major along with sector peer Shell after cutting its forecasts for crude prices over the next three years.The bank has lowered BP from 'overweight' to 'neutral', cutting its target price from 575p to 500p. Shell is still rated 'overweight', although its target has also been trimmed, from 2,700p to 2,500p.JPMorgan has reduced its per-barrel estimates for Brent crude for 2014, 2015 and 2016 to $100, $82 and $88, respectively, from $111, $115 and $120 previously."This revised price outlook resets close to the Brent futures strip averages 2015-16 $86-$88 per barrel. Importantly, it also anticipates a price range down to the $60s for Brent in the first quarter assuming OPEC does too little too late," it said.As for the oil-producing sector, the bank said it sees a "grim" outlook with stocks historically performing the worst in the fourth quarter than in other quarters."If our negative oil price view is correct, the message to equity investors could not be clearer - stand back from this sector, it will look even cheaper in three-months' time and it is not too late to sell," JPMorgan said."Come that point, there could be a compelling time to buy, in our view, especially if Big Oil embraces the need for more fundamental change as believe it now must - we look for fourth-quarter results to confirm this."BP was broadly flat at 441.5p by 14:40 on Monday, while Shell was up 0.8% at 2,247.5p.