The sale of ammunition must be regulated if a global weapons treaty is to be effective, Oxfam has said.
Countries from around the world will gather in New York in July to discuss an international Arms Trade Treaty to combat human rights abuses and violations of humanitarian law, but the charity is concerned the bullets market may not be included.
Stop A Bullet, Stop A War - an Oxfam report - found the global ammunitions industry for small arms and light weapons is worth £2.7 billion, much bigger than the £1.7 billion trade in the weapons themselves.
Anna Macdonald, head of arms control at the charity, said: "A gun without a bullet is a very large metal stick, basically. Ammunition is literally the fuel of conflict.
"It is absolutely essential that the sale of ammunition is included in the treaty and it is far better regulated. It would be totally irrational to leave it out.
"The trade in ammunition is lucrative, but while the monetary cost of production is low, the price paid in human lives for the trade in ammunition is incalculable. An Arms Trade Treaty which doesn't include the trade in bullets doesn't make sense."
Some 153 countries have voted formally at the United Nations in support of the process, but a handful of states including the United States, Syria and Egypt have recently opposed the inclusion of ammunition in the final treaty text.
Oxfam would prefer wide ranging terms in an agreement rather than watering it down to suit a minority of countries.
Ms Macdonald said: "Strong treaties create clear international standards and they affect the behaviour not only of countries that sign up to them, but also even of countries that don't. Strong treaties gain new members. Weak treaties rarely get stronger.
"It's in no government's strategic interest to have the current situation where the arms trade is out of control and it's too easy for human rights abusers and war lords to get their hands on weapons."