Stock traders spent much of Monday capitalizing on the pending sale of Hawaiian Airlines to Alaska Airlines, boosting shares of Hawaiian’s parent company by 193%.

Shares of Hawaiian Holdings Inc. closed Monday at $14.22, up from $4.86 Friday before leaders of the two companies announced the acquisition deal Sunday.

Trading volume spiked to 35.4 million shares Monday, compared with more typical recent daily volume around 2 million or 3 million shares.

Monday’s closing price, however, was well below the agreed-upon purchase price of $18 a share, which Alaska Air Group Inc. plans to pay in cash to Hawaiian Holdings shareholders around 12 to 18 months from now if regulatory and shareholder approvals can be obtained.

Typically in company acquisition deals such as this one, the stock price of the company being acquired rises close to the purchase price unless there are significant uncertainties about the deal being realized or the price changing.

Bloomberg News reported Monday that some stock analysts believe traders may be concerned that the deal might not clear regulatory hurdles.

Leaders of the two airlines suggested in presentations to stock analysts Sunday that they don’t expect anti-competition issues to get in the way of obtaining regulatory approval, in large part because the two companies, with around 1,300 daily flights between them, have only 12 overlapping routes.

“From a competitive standpoint, I think that that lands really, really well,” Alaska Airlines CEO Ben Minicucci said on a Sunday conference call with analysts.

The two companies also noted that a combined operation also would have a little over 50% market share in Hawaii and would allow Hawaii travelers to reach more mainland cities using a combination of flights from the two companies, which would maintain separate brands but operate as one.

Analysts Helane Becker and Thomas Fitzgerald at New York-based investment banking firm TD Cowen said in a Monday research report that they aren’t convinced the U.S. Department of Justice will approve Alaska Air’s acquisition given the agency’s pushback on a pending deal between JetBlue Airways and Spirit Airlines. Still, they said in the report that they think Alaska Air’s deal should be approved, and they expect shares of Hawaiian Holdings will move close to $18 and then stay there if the regulatory approval is granted.

Regarding the purchase price, Alaska Air Chief Financial Officer Shane Tackett told the analysts that paying $1 billion for Hawaiian Airlines stock at $18 a share is fair.

Tackett also described the deal as having a “great valuation” given that the $1.9 billion value, including the assumption of $900 million of Hawaiian Airlines debt, represents a 0.7 multiple of Hawaiian Airlines’ revenue over the past 12 months. That compares with an average 1.7 multiple for five other industry acquisitions over the past 20 years, including Alaska Air’s 2016 acquisition of Virgin America.

The purchase price was agreed to Saturday by board members of Seattle-based Alaska Air and Hawaiian Holdings, a kamaaina company founded in 1929.

Peter Ingram, Hawaiian Airlines president and CEO, told the analysts that the deal is a good one for shareholders in the company.

“We believe this all-cash transaction will deliver significant, immediate and compelling value to our shareholders,” he said on the Sunday conference call.

Shareholders of both airlines are expected to vote in early 2024 on whether to approve the acquisition.

Shares of Hawaiian Holdings last traded around $18 in mid-2022 but have been on a choppy descent since then. Over the past decade, the company’s stock price came close to $60 in 2016 but also fell to around $9 in early 2020 as impacts from the coronavirus pandemic emerged.

The largest shareholders in Hawaiian Holdings are Blackrock Inc., U.S. Global Investors Inc. and Vanguard Group with a collective stake over 30%.

Several law firms announced Monday that they are investigating whether Hawaiian Holdings board members are shortchanging shareholders.

Alaska Air said in its presentation that the purchase price represents an “attractive” premium for Hawaiian Holdings shareholders.

Each company retains options to terminate the deal, but at a cost, according to documents filed Monday with the U.S. Securities and Exchange Commission.

For instance, Hawaiian Holdings would have to pay Alaska Air $39.6 million under circumstances that include backing out of the sale in favor of a superior proposal, and Alaska Air would have to pay Hawaiian Holdings $100 million under circumstances that include the government blocking the acquisition.

Both companies have outside financial and legal advisers on the transaction. For Hawaiian Airlines its financial adviser is Barclays, and its legal adviser is Wilson Sonsini Goodrich &Rosati Professional Corp. Alaska Air has two financial advisers, BofA Securities and PJT Partners, while O’Melveny &Myers LLP is its legal adviser.