"But in the end the prize is significant, and I think the countries can see that this is the big game in town."
There was unified commitment to try to get a deal done.
TPP negotiators will be meeting as early as next week in a country yet to be decided.
The leaders also confirmed they wanted the Trans Pacific Partnership deal to be comprehensive.
Asked if Japan's Prime Minister Shinzo Abe had accepted that meant a total elimination of tariffs, Mr Key said "yes".
He said he had had a long discussion with Mr Abe before the meeting, "and I have got to say he was thoroughly refreshing in his view about his desire to see Japan sign up to TPP, what it might mean".
The statement issued by the leaders after the meeting acknowledged interest from other countries in joining the TPP - South Korea and Thailand have expressed an interest - but it is clear that no new countries will get in until a deal is concluded.
Mr Key said agriculture was one of the sensitive issues to be discussed, by no country was saying it should be part of the agreement.
Secretary of State John Kerry and Trade Representative Mike Froman represented the United States at the meeting,. Mr Obama stayed at home to battle the continuing budget crisis.
Mr Froman said in Bali last week he wanted to resolve outstanding issues, particularly on intellectual property, environment, state-owned enterprises and market access.
Mr Key has said it would be better to wait a bit longer to get a high quality deal rather than meet the end of year deadline with a lower quality deal.
And he still would "bet the ranch" on getting the deal done by the end of the year.
He was more optimistic after yesterday's meeting.
He is also indicating he wants a deal done as soon as possible so he can publicly discuss the detail at home in the face of vocal opposition.
"We want to engage with transparency with the New Zealand public," he said.
"Like a lot of these issues, left in a vacuum people can create uncertainty and therefore a fear factor which is very difficult for us to combat until we can go through point by point and say here is the counter-argument."
The sooner a deal was finalised, the sooner he could engage in discussing it in more detail with the New Zealand public.
Trade talk participants
* Trans Pacific Partnership negotiations began in March 2010.
* 12 countries are negotiating: US, Canada, Mexico, Peru, Chile, Australia, New Zealand, Singapore, Malaysia, Brunei, Vietnam, Japan.
* Among TPP countries, NZ has free trade agreements with Australia, Singapore, Brunei and Chile, Vietnam and Malaysia.
* TPP would give NZ a free trade agreement with the US, Japan, Canada, Mexico and Peru.
