As gateway cities' downtowns revive and thrive, office rents are rising. So we asked Colliers International which commercial business districts across the country have the highest average class-A office rents. While we expected New York City to dominate the list of the top 10 cities with the highest office rental rates, followed by San Francisco, we also found some surprises. For instance, renting office space in Downtown Manhattan costs approximately $22 per sq. ft.