Talks to try and end a pay row between fuel tanker drivers and their employers have been adjourned without the deal needed to halt strike action.
Unite, the union representing the drivers, called the talks "helpful".
The current strike and picket lines have affected petrol stations across the UK, with some running out of fuel.
Talks will now resume for a second day on Tuesday with drivers threatening a second four-day stoppage for this weekend unless an agreement is reached.
Union officials were meeting with managers from two haulage firms, Hoyer UK and Suckling Transport, which are contracted to Anglo-Dutch oil firm Shell.
"I don't think we should kid ourselves there's a lot of work to be done"
The strike, which started on Friday and is due to finish at 0600 BST on Tuesday, has affected 284 of Shell's outlets and 120 have had to stop selling fuel.
More than 600 of all the 8,700 petrol stations in the UK had run out of unleaded and diesel fuels.
Shell runs 10% of the country's fuel stations, but industry sources suggest its market share could be as much as 17%.
Nationwide
Drivers have mounted picket lines at 14 terminals and fuel sites across the UK, including Shell's Stanlow Oil Refinery in Ellesmere Port and the Texaco plant at Pembroke Dock, Pembrokeshire.
Tanker drivers from companies not involved the dispute have joined Shell drivers' at the picket line.
In Scotland, drivers working for other firms have also joined picket lines.
At the Grangemouth fuel depot, drivers working for other companies walked out and joined the Shell drivers' picket line, reported BBC Scotland transport correspondent Louise Batchelor.
This followed news that 11 drivers employed by Scottish Fuels had been suspended for failing to cross the picket line,
Cardiff, Cornwall and parts of London and the West Midlands have been badly hit by petrol stations running dry.
By Monday lunchtime, 616 petrol stations out of 8,700 in England, Scotland and Wales were out of standard fuels, the Department for Business, Enterprise and Regulatory Reform said.
This was lower than the 647 stations affected at the end of Sunday.
Brighter outlook?
The BBC's Martin Shankleman said the fact that talks had been resumed were grounds for fresh optimism.
Bernie Holloway, a director at Hoyer UK - one of the haulage firms affected - told the BBC he was glad that the two sides were talking again.
THE SHELL PAY STRIKE
But he added: "I don't think we should kid ourselves there's a lot of work to be done, but we're hopeful and I'm sure that Unite and ourselves will be giving everything that we can to try and get this issue resolved."
The haulage companies have said unions rejected a pay offer taking the drivers' average salary to £41,500 by January 2009.
However, Unite says the offer would have increased salaries from just under £32,000 to £36,000.
The union also says it is in dispute with Shell because the oil giant dictates the structure and price of the tanker contracts, and therefore has the financial might and influence to affect the ultimate pay levels.
Len McCluskey, assistant general secretary of Unite, said: "We're hoping and we'll be working hard to try and conclude a satisfactory resolution to the dispute."
Business Secretary John Hutton said the negotiations were an encouraging step forward.
He added: "I hope it is possible for the two sides to reach an agreement so as to avoid any repetition of this weekend's disruption."
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