The main share index OSEBX -- which includes a large number of shares linked to the oil industry -- reached 637.76 points by midday.
Last summer another all-time high of 633.24 points was recorded, according to financial news site hegnar.no, also on the back of higher oil prices.
"Asian markets are all up Tuesday morning. That can help European markets, at least in the opening minutes today. With the markets closed since Thursday investors need time to get updated," Roger Berntsen, an analyst at Netfonds Banks, wrote ahead of the opening.
"Among other things, oil prices have risen by four percent during this period while the dollar was strengthened by 1.5 percent," he added.