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As of now only US firm Duke Energy, European company International Power SA and China Huadian Corporation are still participating.
Recently reelected Colombian President Juan Manuel Santos plans to use proceeds from Isagén's sale to finance his ambitious nationwide highways project known as 4G.
"This was a clear point of Santos' reelection campaign," Jairo Agudelo, equity research head at Bancolombia, the country's biggest bank, said.
"He still needs the financial resources. So whether or not local firms are involved, we believe the tender will still go through,"
Agudelo did note that, in exiting, local entities EPM and Grupo Argos both cited an insufficient estimated return on capital.
"It makes us wonder how the market's expected price compares to what the government is asking," Agudelo said.
Opponents of the sale have filed a raft of legal actions against the tender, some of which are still under judicial review.
However, Bancolombia energy analyst Diego Buitrago was confident the sale would go ahead.
Buitrago said: "Colombian courts have already ruled several times in favor of continuing Isagén's tender. There may be delays, but with Santos in power the tender will be completed."
Following its departure from the tender, EPM reportedly plans to sell its 13% stake in Isagén.
EPM argued that new management would create uncertainty on future Isagén dividends and that EPM's investment would be better placed elsewhere.
A sale by EPM of its stake would be subject to approval by local authorities.