The revenues generated by conference events held in Bulgaria have increased 25% over the past 3 years, said the Bulgarian Convention and Visitors Bureau (BCVB). There is no official data on the exact value of conference tourism revenues. The BCVB estimates are based on information provided by hotels hosting conference events as well as four large conference centers, the National Palace of Culture, Inter Expo Center, the Plovdiv International Fair and the Festival Complex in Varna.