Drivers bought nearly 1.48 billion litres of petrol in July 2013 - an 8% fall on the June 2013 figure.
This was only 45 million litres more than the record low in February this year.
July 2013 sales of diesel were down 5% on June's, dropping to just over 2.21 billion litres. These figures include commercial usage.
AA president Edmund King added: "It's staggering that when brilliant weather sent consumers into the shops and gave the UK's retail sector a strong boost, the complete opposite happened at the pumps.
"Not only are petrol sales shadowing the record lows of this winter, but are lower than last July which included the Olympics opening ceremony and football."