The magnitude of the power loss and the flooding raised the possibility that several major oil refineries would take more than a week to reopen. As a result, gasoline prices will probably spike around the country, even if oil prices continue to ease on international markets. Overnight, prices rose an average of 5 cents a gallon, to $3.73 for regular gasoline, according to AAA.

The expectations at nightfall Friday that a virtual tsunami of 20-foot waves would crash directly into Galveston, a city of 57,000, were fortunately dashed after midnight when the eye of the hurricane hit shore. City officials estimated the seas rose about 12 feet, though some tide gauges showed a 15-foot rise, and federal officials said it would take time to determine the exact number.

Whatever the height of the surge, longtime residents of Galveston said the damage was still the worst they had ever seen.

More than two million people evacuated coastal areas of Texas and Louisiana before the storm struck, but the authorities estimated that more than 100,000 people throughout the region, including 20,000 in Galveston, had disregarded mandatory evacuation orders.

For industries in the area, officials at refining companies said early damage reports were encouraging, because the center of the storm missed the refineries. The surge of water into Galveston’s shipping channel, an important depot for imported oil, was not as strong as many had feared, and officials hope to reopen it early in the week if no major obstacles are blocking shipping lanes.

Image Bret Simon, of Galveston, Tex., examining damage along Seawall Boulevard. Credit... Béatrice de Géa for The New York Times

At least 100,000 homes were inundated by surging waters, while isolated fires broke out around the region when trees and flying objects fell on electrical transformers, causing sparks.