* Fourth round of wage talks to fail
* Strike two years ago firmed oil prices (Adds background)
OSLO, June 4 (Reuters) - Wage talks between oil companiesand the largest union representing land-based oil workers inNorway have broken down and are heading to state-appointedmediation, the Norwegian Oil and Gas Association said onWednesday.
The negotiations over pay and work conditions affect about5,000 employees working for Statoil, BP,ConocoPhillips and Shell, among others.
This is the fourth round of talks involving oil workers tohead for mediation. So far talks between the companies andplatform workers, oil services employees and those operatingonshore supply bases have failed to agree a deal.
"Industri Energi did not accept our last offer and chose towalk out of the talks while Safe, Parat and Negotia asked formore time," the Norwegian Oil and Gas Association said in astatement.
These talks will resume after local unions negotiate theirown deals, the Safe union said in a separate statement.
Two years ago about 10 percent of Norway's offshore workerswent on strike for 16 days, cutting oil output by 13 percent andgas by 4 percent.
The dispute ended when oil companies threatened a fulllock-out and the government stepped in to impose a deal. Thestrike then pushed oil prices above $100 a barrel.
The first mandatory mediation is scheduled for June 16-17and unions said that if talks fail they would shut down twoExxonMobil and one GDF Suez platform withcombined production of about 80,000 barrels of oil per day. (Reporting by Gwladys Fouche; Editing by David Goodman)
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