Hook on Saturday said the Obama administration gave out 20 waivers, while the Trump administration only issued eight. However, many of the countries that received waivers under Obama — including European Union member nations — actually cut their purchases to zero immediately.
"The real issue is not how many exemptions you give, but how many countries continue to import," Hochstein said.
A State Department spokesperson on Wednesday said the oil market was fragile when Trump pulled out of the Iran nuclear deal, and the waivers prevented a price spike. The department restated Hook's comparison to the number of waivers granted under Obama.
"We granted waivers to eight — and two of those countries are already at zero," the State Department said. "We are also much more determined to drive up the costs of Iran's malign behavior; the Obama administration lowered the costs with the Iran deal."
China, India, Turkey and South Korea have taken Iranian crude since the sanctions snapped back into place on Nov. 5, according to tanker-tracking firm ClipperData.
China accounts for the lion's share, taking 576,000 barrels per day in December, ClipperData says. South Korea resumed its purchases this month, recently discharging 300,000 barrels, its first cargo since July.
Japan intends to resume imports of Iranian oil as early as this month, Nikkei reported on Tuesday.
Still, Iran's exports have plunged below 1 million bpd from about 2.5 million bpd before looming sanctions began to bite last year, according to Reuters.
— This story has been updated to include a State Department comment.