RTE radio business editor says "petrol prices are continuing to fall"

Im curious to know what all the factors are that affect petrol prices. There is always something blamed for the price to increase (VAT, Duty, price of Crude, Euro/Dollar rate, Oil speculation/trades on futures etc).

Yet there never seems to be a reason for decreases. If the price of crude goes up, so does the price at the pump. It rarely comes down when the price of crude comes down. There is always something else that keeps it up (weak euro or some other unknown quantity)