Twilight in the Desert: The Coming Saudi Oil Shock and the World Economy by Matthew R. Simmons (Wiley, $16.95) has a controversial thesis: ``The risk is high that twilight may soon descend on oil production in Saudi Arabia.'' The author, a Houston investment banker and longtime energy Cassandra, bases his arguments on a reading of more than 200 technical papers presented by engineers from Saudi Aramco, the national oil company, and its predecessor, Aramco. He reports exhaustively on instances of increasing water encroachment into the oil -- a sign of aging fields -- declining reservoir pressure, and depletion of the oil in the kingdom's most prolific rock strata. If Simmons is correct, the global economy, which gets 11% of its oil supply from the country, is in serious danger. However, even if his interpretation is too dire, noted reviewer Stanley Reed, the book contains ``many valuable insights'' and a basic truth that the world needs to rethink its energy assumptions.