Mohamed Moqbel, 45, a camel owner, is one of these smugglers. He told Al Jazeera that he started this work last month.
"Every morning, I go to Talooq with around 20 camel owners to meet doctors. Then they give each camel owner two oxygen cylinders, and we leave Talooq towards the city. After four hours, doctors meet us in al-Maradei in Taiz to take the cylinders," Moqbel said.
"I get 5,000 rials [$23] for each cylinder, and my camel carries two cylinders at once. So it is profitable work for us, as we get 10,000 rials [$46] a day, but sometimes we do not find cylinders to smuggle.