Royal Mail shares climbed further today to value the company at almost £1.5 billion sterling over its initial flotation price.
Shares in the letter and parcel delivery firm hit a high of 475.3p in early trading - valuing the company at almost £4.8 billion, compared with its £3.3 billion initial valuation on Friday.
The shares closed above 465 pence, a gain of about 2.2% on Friday's 455 pence close, as demand for the newly-privatised company shows no sign of easing.
At that level more than 700,000 small investors who bought stakes for an initial £750 will be sitting on a paper profit of about £300, assuming they did not cash them in on Friday.
Around 150,000 postal workers hold stakes worth more than £3,080 - although they cannot sell them for three years.
Shares in the company have now risen 40% above the 330 pence price the British government valued them at - stoking accusations the company was sold too cheaply.
The flotation was described by Labour leader Ed Miliband as a "fire sale of a great institution at a knock-down price".
Full dealing in the company's shares will begin tomorrow, when all investors can buy and sell shares in Royal Mail. Conditional dealing started on Friday for investors who applied for shares through brokers.
That will be followed on Wednesday by the result of a strike ballot by postal workers in the Communication Workers Union over issues linked to privatisation. CWU members are expected to back industrial action, with any strike set to be held on or after October 23 - the run-up to the busy Christmas period.
Demand for Royal Mail shares remained rampant today, with about 16 million shares changing hands, following Friday's frenzy when more than 100 million shares were traded in the first hour.
Investors have been lured by the promise of healthy payouts, with Royal Mail shares expected to offer a dividend yield of around 4.3% based on today's price.