Survival International has information on the various amazonian tribes threatened with extinction by oil companies  http://www.survivalinternational.org/

In Peru, Perenco holds 100% interest in the licence contract for Block 67 in the Maranon Basin and is responsible for a great deal of environmental/human rights damage in the country. They are a good target for British activists because their headquarters are right here in London. More info  http://www.survivalinternational.org/about/perenco
 http://www.theecologist.org/News/news_round_up/686968/oil_companies_perenco_repsolypf_and_conocophillips_under_fire_over_peruvian_tribes.html

Try a google search of ´Perenco amazon´ you´ll find loads of dirt on them.

You should consider supporting the campaign against BP´s deadly activities in Colombia  http://www.colombiasolidarity.org.uk/campaigns/19-bp

Leigh Day are a law firm that have been pursuing oil companies in Colombia and Peru.
 http://www.leighday.co.uk/our-expertise/international-claims/colombia
 http://www.leighday.co.uk/our-expertise/international-claims/peru

If you´re looking for alternatives to oil exploitation, Ecuador has come up with a truly innovative plan to stop oil exploitation in the yasuni national forest, whilst still securing development for this impoverished country... http://www.liveyasuni.org/

Of course I´m sure you already know about the famous Chevron in Ecuador case, but the case is far from over  http://www.chevroninecuador.com/

Hope this helps!!