Tourism and education were also discussed, with O'Neill suggesting that there was scope for British university students to consider pursuing research in Papua New Guinea, and vice versa.
He also encouraged British travellers to consider PNG as a tourist destination, and invited Cameron to see what was happening in the country for himself.
"There are a number of opportunities for increased cooperation between our countries in trade, investment as well as cultural and educational exchange," he said.
"British people, particularly the young men and women, are avid travellers and we would like to for them to see our country."
Both leaders are scheduled to speak at the United Kingdom - Papua New Guinea Trade and Investment Forum tomorrow, where opportunities in PNG's key sectors will be highlighted to prospective investors.
O'Neill said there was increasing interest from European and North American investors about the potential of PNG, and hopes the Forum would entice interested parties to invest in sectors in most need of development, like tourism and agriculture.
"Sources for investment in PNG continue to expand beyond our traditional markets, particularly with LNG production and mining opportunities," he said.
"PNG offers investment potential with an expanding economy that is withstanding the impact of global economy challenges, and has a demonstrated stable political environment."
O'Neill will head to France after the Forum, where he will meet with European Commission president Jean-Claude Juncker and French Foreign Affairs and Immigration Minister Laurent Fabius before speaking with the senior management of Total - operator of the Elk Antelope project, and Puma Energy, at a business breakfast.