Lombarda and two years later, in 1936, he married Greta Paulas, in Vienna. After acquiring an accountancy qualification, he enrolled at Università Cattolica del Sacro Cuore in Milan. In May 1943, he met the Christian Democracy leader Giuseppe Spataro, who introduced him into anti-Fascist circles in Milan against the Italian fascist regime of Mussolini. After 25 July 1943, when Mussolini was forced to resign, Mattei joined a partisan group of the Italian resistance movement in the mountains around Matelica, supplying them with weapons. He was able to join the resistance, despite suspicion over his former membership of the Fascist party. His role was rather marginal, concentrating mainly on administering and organising activities. After a number of roundups, he escaped to Milan. Impressed by his organisational and military skills, Christian Democrats put him in command of their partisan forces. On 26 October 1944, he was captured in Milan, along with others, at the Christian Democrats' secret headquarters in Milan. Detained at the military barracks in Como, he was able to escape on 3 December 1944, taking advantage of a confusion caused by a short circuit which he himself may have engineered. Mattei participated in the North Italian military command of the National Liberation Committee ( – CLN) on behalf of the Christian Democrats. He was decorated by the United States with the Silver Star. Agip and ENI In 1945, the National Liberation Committee appointed him to the leadership of Agip (Azienda Generale Italiana Petrolio – General Italian Oil Company), the national oil company created by the Fascists, with instructions to close it as soon as possible. Mattei instead worked hard to restructure the company and transform it into one of the nation's most important economic assets. In 1949 Mattei made an astonishing public announcement: the soil of the Po Valley in Northern Italy was rich in oil and methane, and Italy would solve all its energy needs using its own resources. Through the Italian press, he then encouraged the idea that the nation (still suffering from the consequences of defeat in World War II) would soon become rich. Agip's financial value immediately grew in the stock exchanges, and the company (owned by the state but operating as a private company) became at once solid and important. The reality was a little different; in the territory of Cortemaggiore, in the Valley of Po, a certain amount of methane had been found together