Coast guard commissioner Jody Thomas called the agency's handling of the spill "excellent" while city manager Penny Ballem stopped short of outright criticizing its response in a report to council.
The spill dumped at least 2,700 litres of bunker fuel into English Bay last week.
Ballem expressed frustrations about the limited information that trickled out in the hours following the spill.
"There are lots of questions we're going to have, and probably lots of benchmarks that we're going to want to have a look at to see: Was this response adequate?" she said Tuesday.
The MV Marathassa was on its maiden voyage to pick up grain from Vancouver when it began leaking fuel last Wednesday. A recreational boater called 911 at 5 p.m. but the city was not notified until 5 a.m. Thursday.
Thomas defended the response at a news conference, where she disputed statements by Environment Minister Mary Polak, who had chastised the coast guard for not immediately assuming control of the spill.
"She is incorrect," Thomas said. "Coast guard was running instant command from Wednesday evening."
Thomas has said a Port Metro Vancouver vessel confirmed a sheen in the bay at 5:38 p.m. and the coast guard performed its own assessment over the following hour.
The coast guard alerted Western Canada Marine Response Corp., an industry-owned company responsible for cleanup, to stand by for a possible response at 6 p.m. The WCMRC was officially activated at 8 p.m. and arrived on scene at 9:25 p.m.
Ballem said the city must look at international standards before judging whether the response was quick enough. But she voiced strong concerns about how long it took for information to be relayed to the public — including 48 hours to identify the substance as toxic bunker fuel.
She added the coast guard only called Vancouver police at 9:53 p.m. to see if the department had heard any additional reports of an oil spill — which it had not.
Ballem's report also said an oil-absorbing boom was secured around the vessel at 5:53 a.m. Thursday, in contrast with the coast guard's previous statements that the boom was in place by midnight.
While Thomas estimated that 90 per cent of the spill has been cleaned up, Ballem said the city has no way to verify that figure.
"What I understand from scientists is that it would be extraordinary to recover 80 per cent in a spill like this," Ballem said.
The coast guard's estimate of 2,700 litres of fuel that was leaked is likely to rise to as high as 5,000 litres, Ballem said.
The ship's owners will face prosecution to recover cleanup costs and have hired as their agent global company Polaris, which is now doing the environmental assessment.
Ballem said the city has hired consultants to test the water and sediment near the bay's surface to ensure they have independent information.
There is a $28-million liability cap on the ship owner's contributions, while $162 million is available through the Canadian Ship-Source Oil Pollution Fund, which can be used if owner contribution caps are exceeded.
"There's no guarantee that we will get every nickel we have spent," Ballem said.
Mayor Gregor Robertson told reporters outside council chambers that the coast guard's slugglish response is the "direct consequence" of federal cuts that saw the nearby Kitsilano coast guard quietly closed in February 2013.
He said he has serious concerns about larger spills as tanker traffic is only expected to increase.
"For a small spill, it was a slow response," he said. "For a large spill, it's unthinkable how much damage would be done in those initial hours."
— With files from Tamsyn Burgmann