Despite weak demand, more new office space entered the Southern Nevada market in the fourth quarter, pushing the total inventory to 51.6 million square feet, reports Las Vegas-based business advisory firm Applied Analysis. Valley vacancy rates hit 25.3% at the end of 2011, as a result, which is the highest amount of empty office space in over 5 years. “The nosedive in demand that has occurred during the past four year and the oversupply conditions that persist will require nearly a decade of improvements before vacancies reach pre-recession levels,” said Applied Analysis principal Brian Gordon.