After her exposé on Standard Oil and character study of John D. Rockefeller, she wrote biographies of businessmen Elbert Henry Gary, chairman of U.S. Steel, and Owen D. Young, president of General Electric.

A prolific writer and lecturer, Tarbell was known for taking complex subjects — such as the oil industry, tariffs, labor practices — and breaking them down into informative and easily understood articles.

Tarbell also traveled to all of the then 48 states on the lecture circuit and spoke on subjects including the evils of war, world peace, American politics, trusts, tariffs, labor practices, and women's issues.

[29] Tarbell also led the charge to place a sophomore stone on campus dedicated to learning and with the Latin phrase, Spes sibi quisque, which translates to "Everyone is his/her own hope".

[28] Tarbell returned to Pennsylvania, where she met Theodore L. Flood, editor of The Chautauquan, a teaching supplement for home study courses at Chautauqua, New York.

[39] She began researching women from history including Germaine de Staël and Madame Roland for inspiration and as subject matter for her writing.

The Eiffel Tower had been finished recently in 1889, and Tarbell and her friends enjoyed the art produced by Impressionists including Degas, Monet, Manet, and Van Gogh.

"[47] Tarbell attended the Can-can at the Moulin Rouge and in a letter to her family she advised them to read Mark Twain's description of it in The Innocents Abroad as she didn't like to write about it.

Tarbell determined that Roland, who followed her husband's lead, was not the independent thinker she had imagined and was complicit in creating an atmosphere where violence led to the Terror and her own execution.

[49][50] She wrote of Roland, "This woman had been one of the steadiest influences to violence, willing, even eager, to use this terrible revolutionary force, so bewildering and terrifying to me, to accomplish her ends, childishly believing herself and her friends strong enough to control it when they needed it no longer.

[12][58] Tarbell made use of Hubbard's extensive collection of Napoleon material and memorabilia as well as resources at the Library of Congress and the U.S. State Department.

[67] She remembered the news of his assassination and her parents' reaction to it: her father coming home from his shop, her mother burying her "face in her apron, running into her room sobbing as if her heart would break.

"[76] Having recently published a series on crime in America and looking for another big topic to cover, Tarbell and the other editors at McClure's decided to look into the growth of trusts: steel and sugar were both considered[77] before they settled on oil.

The documentation and oral interviews she gathered proved Standard Oil had used strong-arm tactics and manipulated competitors, railroad companies and others to reach its corporate goals.

[82] A subhead on the cover of Weinberg's book encapsulates it this way: "How a female investigative journalist brought down the world's greatest tycoon and broke up the Standard Oil monopoly".

An office boy working at the Standard Oil headquarters was given the job of destroying records which included evidence that railroads were giving the company advance information about refiner's shipments.

She investigated Standard Oil and Rockefeller by using documents— hundreds of thousands of pages scattered throughout the nation—and then amplified her findings through interviews with the corporation's executives and competitors, government regulators, and academic experts past and present.

[2] President Theodore Roosevelt gave Tarbell and her peers including Lincoln Steffens and Ray Stannard Baker the label, "muckrakers."

[94] Tarbell wrote of the work required on a farm: "Things happened: the roof leaked; the grass must be cut if I was to have a comfortable sward to sit on; water in the house was imperative.

"[100] She was fascinated by Thomas Lynch of the Frick Coke Company, who was committed to providing decent living conditions for his workers and believed that "Safety First" was preferable to accidents.

[108] Historian Robert Stinson believed that she was making new public statements about the ambiguity she had lived in her own life, which defined women's roles based upon their nature and saw attempts to push the boundaries into men's realms as unnatural.

[108] The book, which was poorly received, contained tributes to early supporters of women including Susan B. Anthony and Elizabeth Cady Stanton.

[113] Tarbell joined the Chautauqua Science and Literary Circuit, a lecture and entertainment tour filled with public speakers, singers and other acts such as trained dogs and yodelers.

Other efforts included knitting, sewing, bandage making, and the opening of day-care centers to operate while women began working in factories.

Some of her former McClure's colleagues were also there for the Paris Peace Conference: John S. Phillips as editor of the Red Cross Magazine and Ray Stannard Baker as an assistant to President Woodrow Wilson.

[6] Tarbell was a member of President Wilson's Industrial Conference in 1919, representing the Pen and Brush Club[116] of Gramercy Park, New York City, and served on a committee looking into hours of labor along with Robert Brookings.

[123] Tarbell's final business biography was a profile of Owen D. Young, the president of General Electric and founder of Radio Corporation of America and then NBC.

Everett E. Dennis, Executive Director of the Freedom Forum Media Studies Center at Columbia University stated in 1993 that Tarbell helped invent modern journalism.

[141] Tarbell's writing has been described by a biographer as fair and professional,[143] (though some later observers have been less kind, accusing her of cherry picking data to support her conclusions[144])[verification needed] and her methods have been used widely to train other investigative journalists.

[147] Charles Klein's political play, The Lion and the Mouse (1905), opened soon after Tarbell's series on Standard Oil had been published in McClure's Magazine, and the plot was thought to be based on her campaign.