Verizon's jumbo $25 billion multitranche bond offering could be upsized because of strong investor demand, sources said on Tuesday.
The order book is approaching $100 billion, those sources said. Verizon was initially expected to sell about $25 billion of debt. But with the strong demand, the market is now expecting a $30 billion to $40 billion issue. Management hasn't made a decision yet on the ultimate size of the deal.
Books will close at 3 p.m. on Tuesday.
The deal is already set to surpass Apple's $17 billion debt offering earlier this year, which was the largest on record.
Verizon has launched the multi-tranche debt offering to fund its $130 billion buyout of Vodafone's stake in Verizon Wireless.

(Read more: Why $130 billion Verizon-Vodafone deal makes sense)
The multi-tranche bond deal consisting of three-year fixed and floating notes, five-year fixed and floating notes and four fixed-rate tranches with seven-, 10-, 20- and 30-year maturities, according to a filing with the Securities and Exchange Commission.
The 10- and 30-year tranches are seeing the most demand, sources said.
Barclays, BofA Merrill Lynch, JPMorgan and Morgan Stanley are the active bookrunners on the deal, with pricing scheduled for Wednesday.
— Reporting by CNBC's Kayla Tausche