Shell moved the staff after militants killed 22 people in an attack in the eastern Saudi city of Khobar in May, said a spokesman who asked not to be identified. He declined to give further details. Shell last year was the first western company along with Total SA to win rights to develop Saudi energy reserves since nationalization in the 1970s. International oil companies have been competing to work in Saudi Arabia since the kingdom, which holds a quarter of the world's proven oil reserves, decided to end state-controlled development of its natural resources. Shell, Total and rivals are looking to add reserves to their books amid record oil prices. Shell, Europe's second-biggest publicly traded oil company, is involved in six joint ventures in the kingdom, employing about 2,000 people, most of them Saudi nationals. Among the employees are several westerners, including Floris Ansingh, president of Shell in the kingdom. The issue of security ``has become particularly acute'' following the Khobar attack, in which the joint-venture offices of Shell and Total were attacked, Ansingh wrote in this month's Shell Middle East magazine. The attacks ``have forced Shell staff, and other international companies, to put in place the best possible precautions to protect the safety of all staff,'' Ansingh wrote, without giving details. At least 34 foreigners, including more than 15 westerners, have been killed since the campaign of violence to drive them out of the country and undermine the ruling al-Saud family, intensified on May 1. Five westerners were killed that day in an attack at an oil- related industrial site at Yanbu on Saudi Arabia's Red Sea coast. A Frenchman working for Thales SA, Europe's biggest maker of military electronics, was the latest westerner to be killed in the kingdom. He was shot dead while driving home at night in the city of Jeddah on Sept. 26. PIN/BLOOMBERG