The Bubbling Under Hot 100 Singles (previously known as Bubbling Under the Hot 100) is a chart published weekly by Billboard magazine in the United States. The chart lists the top singles that have not previously charted on the main Billboard Hot 100. Chart rankings are based on radio airplay and sales. In its initial years, the chart listed 15 positions, but expanded to as many as 36 during the 1960s, particularly during years when over 1,000 singles made the Billboard Hot 100 chart. From 1974 to 1985, the chart consisted of 10 positions; since 1992, the Bubbling Under Hot 100 Singles chart has listed 25 positions.