Columns of black smoke rise from several points along the road in part of northern Syria. Here the smoke is not a sign of air strikes but of crude oil being processed in makeshift refineries. "People started doing it about one year ago but at that time we didn't know how to," says Ahmed, a 35-year-old farmer-turned-refiner. "We got the knowledge from someone from around here who had learned in Saudi Arabia", he says, standing next to a big metal tank containing crude oil. Ahmed and his brother Abdallah, a former driver, started their refinery operation three months ago, along with many other locals, as the regime lost control over oil fields in north and east Syria. Their tank has a capacity of 1,000 litres (220 gallons), though they only make it two-thirds full at a time because the refining process requires air, they say. A fire is lit underneath to heat the tank, eventually boiling the crude, and producing thick black smoke. As the crude boils, various products run off through two tubes which are cooled as they pass underwater through three ponds and then into a container that collects the resulting products. What comes out first, the brothers term "cooking gas", which they simply allow to escape. Next comes petrol, then kerosene used in stoves, then diesel fuel. A Syrian man in the Al Raqqa countryside works on refining crude oil on April 15, 2013 The pair call the final product "fat" and either add it back into the fire under the tank, or occasionally mix it with the diesel for use in some "heavy vehicles." This process is a crude form of the fractional distillation process used at oil refineries around the world, and has proved profitable for the brothers. Boiling and refining a tank takes them about four hours, and they estimate they make a 50-60 percent profit on each barrel, selling the products to locals. "Business is good", Ahmed says smiling, his face and hands blackened by the smoke. The brothers are unlikely to win any health and safety awards. Neither wears gloves nor protective gear, and Abdullah smokes a cigarette on the job. "It's ok as long as you are not right next to the benzene (petrol)," he says matter-of-factly. "We haven't had any (health) problem, nothing will happen to us," he adds with a grin. The brothers get their raw material from the Deir Ezzor countryside, driving two and a half hours in their truck to purchase oil barrels from middlemen or those in control of the oil fields: local tribes and the jihadist Al-Nusra Front. Al-Nusra got involved in the oil business about six months ago, they say. A Syrian man in the Al Raqqa countryside pours crude oil into a pit on April 15, 2013 "Al-Nusra are operating in both lines, business and fighting," Ahmed says. The group has been labelled a terrorist organisation by the United States and its leader has pledged allegiance to Al-Qaeda chief Ayman al-Zawahiri. But on the ground, Al-Nusra has won respect from some locals for its fighting prowess, discipline and ability to organise daily life in rebel-held areas. Ahmed says he's not a fan of the group, buying from them out of necessity. Rebel brigades "Liwa al-Tawhid, Ahrar al-Sham, they are very good guys, but we don't like al-Nusra," he says. The brothers buy crude about three times a week, picking up nine barrels a time. "Each well has a different price, depending on the quality of its oil," says Ahmed. One 2,200-litre barrel runs from 500 to 10,000 Syrian pounds (approximately $5- $1000, but the cheapest barrels only yield about 50 litres of refined products, they say. Local tribes first began controlling oil fields in the Deir Ezzor countryside about a year ago. "People then didn't know how to do this refining, they would use (the crude) as they could, some heavy vehicles can use unrefined oil," Ahmed says. "When these tribes discovered the oil wells, the revolution in Deir Ezzor was over, they used to be poor and it went from revolution to oil industry." Deir Ezzor contains the largest energy reserves in Syria, which produced some 420,000 of barrels of oil a day before the United States and the European Union banned the import of Syrian petroleum in 2011.