The Financial Times has useful information at (click here to view) on commodity prices, including those for crude oil, unleaded 95 gasoline (petrol) and diesel.
The prices quoted are in metric tonnes (weight) rather than volume (litres).

By way of guidance, to arrive at the pence per litre cost of petrol or diesel use the following conversion factors:

• Petrol
  1 metric tonne of gasoline (petrol) = ~1,360 litres
  To convert the US dollar per tonne price to pence per litre, divide the price by 1,360 and multiply the result by the US$/£ exchange rate.
  For example: a price of $1,200 per tonne gasoline and $/£ exchange rate of 0.62:
  1,200 ÷ 1,360 x 0.62 = 54.7p per litre
• Diesel
  1 metric tonne of diesel (10ppm sulphur) = ~1,190 litres
  In the calculation above substitute the diesel conversion factor of 1,190 for the petrol 1,360

• For information on motoring taxation, click on the link below for a study commissioned by the RAC Foundation from the independent Institute for Fiscal Studies. Fuel for Thought, the what, why and how of motoring taxation.
• For a copy of the  'Study of the UK petroleum retail market' by Deloitte for DECC, published on 14 December 2012, click here.
• For the OFT report on the UK petrol and diesel sector, please click here.