In the capital Madrid, tension mounted as riot police detained a group of striking truckers who refused to unblock a main city road.
Police officers seized keys from the trucks and took the pickets away leaving their vehicles behind.
However, there was some hope on Wednesday that the strikes may soon come to an end.
Magdalena Alvarez, Spain's infrastructure minister, told parliament that the government and the main group representing strikers had agreed terms, not yet outlined, to end the blockades.
Many parts of Spain are suffering fuel shortages as protesters continue to picket fuel depots.
Some market stall holders, particularly traders in fruit, vegetables and fish, say they only have supplies for another day or two.
The strike is also beginning to limit restaurants' supplies.
"The effects of the strike, already on its third day, are making themselves felt. Our refrigerators will soon be empty", Felix de la Fuente, a restaurant owner said.
Despite the shortages, Juanjo, a Madrid resident, expressed his solidarity with the strikers and said he understood their motives.
"I guess they considered it necessary, that's probably the case. They don't have other options, if I were a lorry driver I would most likely join the strike.
"Actually, as a driver I already feel it too so it also affects me," he said.
Portuguese drivers have joined the strike and there have also been protests in France over the impact of record oil prices, now at highs of more than $139 per barrel.
On Tuesday, one striking truck driver was run over by a van and killed near a Granada market in southern Spain, while in Portugal, a striker died as he tried to stop a truck on a road north of the capital Lisbon.