The host, British Prime Minister David Cameron, has pushed for more sharing of financial information among countries. In his final pre-summit declaration, Cameron said his country would lead by example by setting up a registry that reveals who is behind so-called "shell companies" that obscure their true owners.
Cameron is being joined by President Barack Obama, Russian Prime Minister Vladimir Putin and the leaders of France, Germany, Italy, Canada and Japan.
Cameron said all G-8 members must cooperate more to restrict companies' ability to exploit foreign tax shelters, including Britain's own crown dependencies and far-flung overseas territories, as a way to boost government revenue and economic growth.
"These issues corrode public trust and undermine a competitive low tax economy which can only be sustained if people actually pay the taxes they owe," he said.
Later Monday, Cameron plans to convene a meeting on reaching agreement on a long-debated European Union-U.S. trade pact. The participants will include Obama, French President Francois Hollande, German Chancellor Angela Merkel, new Italian Prime Minister Prime Minister Enrico Letta, EU Commission chief Jose Manuel Barroso and European Council President Herman Van Rompuy. The EU decided on a negotiating plan for its side only on Friday.
A trade pact would lower tariffs and reduce regulations that serve as barriers to buying or selling goods and services on both sides of the Atlantic. A deal is seen as important for spurring Europe's stagnant economy.
On the G-8 security front, Northern Ireland Chief Constable Matt Baggott said police didn't have to make a single arrest during two anti-G-8 protests and a related outdoor concert Saturday in Belfast.
"We are quietly optimistic based on what we've seen yesterday that this could be the most successful G-8 conference," Baggott told reporters at the summit press center.
A range of socialist and anti-globalization groups plan to march Monday night from the town of Enniskillen to the high steel fences preventing access to the Lough Erne golf resort as G-8 leaders hold a working dinner expected to focus on foreign policy disputes, particularly Syria.
Police have formed a security perimeter around the resort that includes several miles of coiled razor wire and boat-based police units.
Officers spent weeks training in England to face potential crowds exceeding 10,000. But the officer commanding the G-8 security operation, Assistant Chief Constable Alistair Finlay, said intelligence estimates put the expected number of protesters Monday night at just 2,000.
He said few hard-core socialist protesters who targeted past G-8 summits in Europe had traveled to Northern Ireland from continental Europe. He said police believe many this time have traveled instead to Turkey to join anti-government demonstrations there.