The Scottish government in January said there are around 24 billion barrels of oil to be recovered from the North Sea. The government estimated the wholesale value of the reserves at $2.4 trillion.
It expects oil and natural gas would add to the federal coffers of an independent Scotland. A vote for independence from Great Britain is scheduled for next year.
Ewing told energy reporting website Rigzone during an energy conference in Houston that offshore Scotland presented significant opportunities to explorers.
"My personal view is that oil and gas production (offshore Scotland) will continue for the rest of the century provided we make the right policy decisions," he said.
BP announced in March that it joined Chevron, ConocoPhillips and Shell in a decision to move forward with plans for a third phase of operations at the Clair oil field west of Shetland.
Phase 1 development has produced 90 million barrels of oil since operations began in 2005. Phase 2 is expected to produce reach peak production capacity of 120,000 barrels of oil per day after operations begin in 2016.
"The Clair field was actually discovered in 1977 and that's ironic because we were told by London that the oil would run out in the '90s," Ewing said.