Like President-elect Donald Trump's first press conference since securing victory, Wall Street's trading on Wednesday was unpredictable. Stocks scored slight to modest gains after flitting between losses and gains in the hours after Trump took the stage. 

The S&P 500 gained 0.28%, and the Dow Jones Industrial Average added 0.50%. The Nasdaq was up 0.21%, securing a new record close of 5,563. The CBOE Volatility Index (VIX.X) spiked to more than 12 on Wednesday.

Biotech stocks sold off shortly after Trump suggested he would aggressively negotiate the prices the U.S. paid for drugs. In his first press conference since July, Trump said pharmaceutical companies have been "getting away with murder." The iShares Nasdaq Biotechnology ETF (IBB) slumped more than 3%, while the SPDR S&P Biotech ETF (XBI) slid 3.5%.

Lockheed Martin (LMT) also declined after Trump reiterated that his presidency would seek to cut costs in the construction of a new Air Force fleet. Trump had previously criticized the costs of the F-35 program.

Trump repeated a number of his previous talking points, including that he would not release his tax returns as they were under audit and that only the press cared about the issue. Trump also noted that the president cannot have a conflict of interest.

Trump also pointed out the potential that intelligence agencies could have been behind the leak of unverified reports of his links to Russia on Tuesday, despite no evidence. Trump called the reports "fake news."

Trump's election in November has lit a fire under stocks, particularly the Dow. Since the day after the election in November, the Dow has rocketed more than 8% higher on the hopes of higher construction spending in the U.S. and loosened regulations on Wall Street. The Dow last week came within a point of the 20,000 milestone before backing off.

"On the spending side, the equity market appears to expect large health care cutbacks, but has moderated its initial post-election expectations for increased infrastructure spending," Goldman Sachs analysts wrote in a note on Wednesday. "On the tax side, the equity market appears to expect corporate tax cuts, but the evidence that a switch to a border-adjusted tax is even partially priced is only mixed."

Merck (MRK) rose nearly 3% after one of its lung cancer treatments gained progress toward going to market. On Tuesday evening, the drugmaker said the U.S. Food and Drug Administration had allowed a priority review for Keytruda as a lung cancer treatment.

Crude oil prices rebounded Wednesday despite a weekly reading on inventories showing an increase nearly four times what analysts had expected. U.S. crude stocks rose by 4.1 million barrels in the past week, partially reversing a drop seen a week earlier. Analysts had expected inventories to rise by 1.2 million barrels. Gasoline and distillates stocks also rose faster than expected.

The U.S. Energy Information Administration on Tuesday increased its forecast for U.S. crude output this year to 9 million barrels a day, up from 8.78 million in its previous forecast. A weekly report on Friday showed U.S. drilling activity increase for the 10th consecutive week in a row.

West Texas Intermediate crude was up 2.8% to $52.25 a barrel on Wednesday.

Workday (WDAY) climbed 9% after Walmart (WMT) signed up for a subscription. The world's largest retailer will use the company's human capital management and recruiting tools.

Volkswagen (VLKAY) rose 4% after reportedly securing a plea deal worth $4.3 billion with U.S. regulators for its emissions-rigging scandal. The settlement includes a $2.8 billion criminal fine. Volkswagen also reportedly admitted guilt in deceiving regulators since 2006.

Signet Jewelers (SIG) fell 2% after reducing its profit and sales targets for the critical holiday season. The jewelry retailer anticipates fourth-quarter adjusted earnings of $4 to $4.05 a share, down from its previous high-end range of $4.20. Same-store sales are anticipated to have fallen 4.8% to 4.3%. The company said its underperformance was driven by weakness in its Sterling e-commerce business.

Supervalu ( SVU) reported a disappointing quarter, swinging to a surprise loss and posting a drop in same-store sales. The grocery store chain reported a 5.7% drop in same-store sales, a sharper decline than an anticipated fall of 4.7%. Overall revenue fell 1.4% to $3 billion, falling short of $3.79 billion consensus.

American Airlines (AAL)  rose by less than 1% after reporting December traffic numbers. Load factor slipped to 80.6% in December from 81.6% a year earlier, while traffic fell 0.8% and capacity increased 0.5%. The airline anticipates total revenue per available seat mile to come in flat to a 2% decline over the fourth quarter.

Exxon Mobil (XOM) was downgraded to market perform from outperform at Wells Fargo. The firm said the oiler trades at a premium valuation and will likely struggle to find attractively valued assets to acquire.

Boeing (BA) could conduct involuntary layoffs of engineers as part of cost-cutting measures, according to an internal memo obtained by Reuters. Other voluntary layoffs in Washington state, southern California and South Carolina are also possible. The measure is in response to increasing competition and slowing sales.

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