Mr Zoellick says the Iraq war has not soured relations
World economic leaders have said they have achieved "an unambiguous sense of commitment" to liberalising international trade.
Representatives of several dozen governments - including almost all industrialised nations - have been discussing reform of world trade at the Paris meetings of the Organisation for Economic Cooperation and Development (OECD).
As the meetings concluded, leading participants were unanimous in claiming that the political will for a new worldwide trade regime had been strengthened.
But most important sticking points, notably concerns on the part of developing countries and the continuing absence of reform to the EU farm subsidy regime, have yet to be tackled.
Substantial agreement is seen as crucial ahead of a meeting of the World Trade Organisation (WTO) in Mexico in September.
Robert Zoellick, the US trade representative, and European trade commissioner Pascal Lamy, separately insisted that they had made strides in identifying the key areas for discussion.
The two men are to meet informally on Thursday "to compare notes", Mr Zoellick said.
Mr Zoellick said that the atmosphere between Europe and the US had not been soured by disagreements over the Iraqi war.
But he also argued that a major obstacle in any global trade reform was Europe's common agricultural policy (CAP), which subsidises European farmers and effectively raises barriers to non-EU farm products.
The European Commission has committed itself to reform of the CAP, but some individual EU member countries have yet to sign up.
Calls for flexibility
The other main sticking point - calls from developing countries for preferential access to Western markets - has also been under discussion at the OECD.
Although there is substantial agreement on removing tariffs from most industrial products, developing countries are involved in a complex series of often bilateral talks on agricultural commodities.
The WTO director general, Supachai Panitchpakdi, warned that not all countries were being reasonable in their expectations.
And Mr Zoellick said some developing countries needed to be more flexible, pointing out that 70% of the trade tariffs they pay are to other developing countries.
Without being specific, Mr Supachai said he was leaving the meetings happy.
"Some countries have indicated their willingness for a greater degree of flexibility."
Ups and downs
Mr Zoellick also said progress had been made in Russia's application to the WTO, which some hoped to complete by the end of this year.
Mr Zoellick had a two-hour meeting in Paris with Alexey Kudrin, the Russian Finance Minister, which he said had been "fruitful".
But despite the generally positive feeling, some delegates were disappointed at the lack of demonstrable progress.
World trade talks have resulted in a series of let-downs, notably the failure to meet an end-March deadline for a framework agricultural agreement, and continuing disagreements over access to medicines in poor countries.
Helen Clark, the New Zealand Prime Minister, who is chairing the OECD meeting, said this current round of trade talks was a "once-in-a-generation opportunity which we cannot afford to miss".