U.S. companies continued a shopping spree for their own shares in May, making $173.6 billion in buyback announcements, the highest monthly total ever, according to a research report.

In May U.S.-listed companies also sold new shares at the fastest pace in three years, but cash takeovers of companies with U.S. listings fell to a three-month low, according to TrimTabs Investment Research.

The high number of buyback announcements was due "in large part" to expected corporate tax savings, it said.

TrimTabs said Apple Inc was the biggest spender, with an announcement for potential buybacks of up to $100 billion, while Micron Technology made a $10.0 billion announcement, followed by Qualcomm Inc.'s $8.8 billion buyback proposal.

Adobe Systems said it would buy $8.0 billion of its stock and T-Mobile announced $7.5 billion in buybacks.

The tally for cash takeovers involving companies with U.S. listings was $27.7 billion, according to TrimTabs. It said that the largest deals were Japanese drugmaker Takeda Pharmaceutical's offer for rival Shire PLC for $9.0 billion and Elliott Management's $6.3 billion buyout bid for Athenahealth.

Underwriters were also active in May, with new equity offerings spiking to a three-year high of $43.6 billion, according to the report. It said that AXA Equitable Holdings' $3.6 billion listing was the largest initial public offering since March 2017.

S&P 500 companies returned a record $1 trillion to shareholders the past year, according to a late May report from S&P Dow Jones indices. It cited a surge in dividends and stock buybacks after sweeping corporate tax cuts introduced by Republicans late in 2017.