Towers Watson's assessment of the sector concluded more insurers might focus on the bulk annuity market if they expect to write fewer individual annuities under the new pensions regime announced in the recent Budget.
Last year was dominated by three big players, with one insurer alone writing half of the market's total premiums.
Towers Watson's latest reported highlighted that in 2013 eight insurers wrote 186 bulk annuity deals worth more than £7.2 billion.

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Some £3.7 billion was written by one insurer, with two other insurers writing £1.4 billion and £1.3 billion respectively.
Towers Watson advised on over half the £7.2 billion total, having advised on deals ranging from £5 million to £1.5 billion.
The research also showed that sub-£10 million bulk annuity deals outnumbered those over £10 million, suggesting the insurers who focus on medical underwriting have the opportunity to significantly increase their share of the total number of deals written.
Sadie Hayes, transaction specialist at Towers Watson, said: "The last year has shown a move towards an even greater domination of the market by a few insurers.
"Rothesay Life's recent announcement of its planned acquisition of MetLife appears to compound this effect further.
"Counteracting this, Just Retirement's and Partnership's share of the market may increase as medical underwriting takes off, perhaps becoming the norm for smaller schemes.
"With the recent Budget announcement on removing the forced annuitisation of defined contribution pots, we expect to see more insurers redirecting capital from their individual annuity business to their bulk annuity business."