American consumers spent more than a billion dollars a day last week during a three-day online sales period, which started with \"Cyber Monday,\" a monitoring firm reported. The firm comScore said that for the holiday season to date, $18.7 billion has been spent online, marking a 15-percent increase versus the corresponding days last year. The most recent week saw three individual days eclipse $1 billion in spending, led by \"Cyber Monday,\" which became the heaviest online spending day on record, the firm noted. On that day alone consumers\' online spending came to $1.25 billion. Tuesday, November 29, reached $1.12 billion, while Wednesday, November 30 reached $1.03 billion, comScore said. These three billion dollar spending days currently rank as three of the four heaviest online spending days in history, according to the firm. \"As the deals from this week expire, it will be important to see the degree to which consumers return to the same retailers to continue their holiday shopping,\" commented comScore chairman Gian Fulgoni.