Saudi Arabian shares dropped for the first time in three days, led by banks after nine euro-region countries lost their top credit ratings at Standard & Poor\'s and two local lenders\' earnings disappointed investors. Arab National Bank headed for its largest drop since October after reporting lower-than-estimated fourth-quarter profit. Saudi Basic Industries Corp., the world\'s largest petrochemicals company, fell for a second day. The Tadawul All Share Index weakened less than 0.1 per cent to 6,482.66 in Riyadh. \"The ratings downgrade for some AAA-rated countries has curtailed optimism that the European debt crisis is heading in an encouraging direction,\" said Asim Bukhtiar, an equity analyst at Riyad Capital. \"The disappointing results from Arab National Bank and Saudi Investment Bank are also weighing on the banking stocks.\"