The most recent private trades in the Swedish company have taken place at above $4,000 per share according to sources.
One of the sources said the recent trades were at a record-high of $4,200, valuing the firm at $19 billion or more. That compares to around $16 billion earlier this autumn.
Spotify is aiming to file its intention to float with U.S. regulators toward the end of this year, sources said.
Also supporting perceptions of Spotify's increasing value, Tencent's (>> Tencent Holdings Ltd) purchase of new Spotify shares implies a valuation of $5,000 per share, one of the sources said.
Spotify and the music arm of China's Tencent Holdings Ltd said last week they would buy minority stakes in each other, but gave no financial details.
Spotify did not immediately respond to inquiries about valuation and listing.
The private market for shares prior to a public listing allows employees and founders of private companies such as Spotify to cash in on some of their paper wealth, while letting other investors get a head start on the listing.
Spotify's valuation when it lists - expected to be within 90 days after filing - is forecast to be a few billion dollars higher than current trades as illiquidity risk tends to depress the value ahead of listing, the sources said.
While several big tech firms have struggled to enter China, Spotify has with the Tencent deal secured an exposure to the growing Chinese music streaming market.
Spotify is the biggest global music streaming company and counts tech giants Apple (>> Apple) and Amazon (>> Amazon.com) as its main rivals.
The timing for its filing with the U.S. Securities and Exchange Commission in December is roughly in line with what has been previously suggested by sources.
Spotify aims to pursuing a so-called direct listing on the New York Stock Exchange, allowing existing investors to sell shares without raising money from new ones, sources have previously told Reuters. The move is also aimed at saving hundreds of millions of dollars in underwriting fees from investment banks.
(Reporting by Olof Swahnberg and Helena Soderpalm, additional reporting by Dasha Afanasieva, editing by Niklas Pollard and Jane Merriman)