The Guardian - Cost rose by 10p a litre to average of 190.5p in October in third worst monthly increase on record. Drivers experienced a severe shock after the price of diesel shot up in October amid the fallout from the Opec+ oil cartel's decision to cut production, the RAC has said.The price of diesel rose by 10p a litre to 190.5p on average the third worst monthly increase on record, behind previous increases this year, data from the motoring group showed.