This article is part of our series, “Women in Optimization.” Although these articles will highlight women, we hope the stories will encourage all individuals who might want to pursue a career in optimization.
“I have called myself the reluctant mathematician,” Dr. Cassandra McZeal begins. “Because I didn't choose math. Math chose me.”
As an undergraduate at Southwestern University, McZeal changed her major several times. Psychology, sociology, pre-med, biology, chemistry—nothing fit quite right. Concerned about graduating on time, she turned to her advisor for guidance.
“Cassandra,” he said, “the only classes you take every semester are in the math department. You are a math major.”
Becoming a Math Major
While the suggestion surprised McZeal, Southwestern University helped her discover her inner mathematician. The same advisor encouraged her to attend a six-week summer program at UC Berkeley, where she discovered that theoretical mathematics was not for her.
Back in Georgetown, Texas for the next semester, faculty encouraged her to attend local American Mathematical Society meetings. There, she met Dr. Richard Tapia, who invited her to spend the next summer in an applied mathematics program at Rice University. Applied math was for her.
After graduating on time, she received a National Science Foundation fellowship and returned to Rice to pursue her PhD in Computational and Applied Mathematics.
Earning a Doctorate & Starting a Family…At the Same Time
McZeal took classes on mathematical optimization and linear programming at Rice and loved it. Previously, she had focused on pure math, solving problems on paper.
“Learning about how to transform matrices so you can actually have them solve faster and better on computers—it was just completely different and totally fascinating to me,” McZeal recalls. She had found her fit.
Her thesis, which she completed under the guidance of supervisor Dr. Bob Bixby, was titled “Reoptimization in Interior-Point Methods with Application to Integer Programming.” Completing a dissertation is demanding enough on its own—not to mention she gave her defense just three months after giving birth. Thankfully, she once again had community support.
“[My office mate and I] both had babies within six months of each other. And so we had a Pack ‘n Play in our office, and I would watch her son if she had to attend a meeting on campus, and she would watch my baby. It was great. We had a great little ecosystem amongst the graduate students at Rice.”
Following graduation, she did a one-year postdoctoral fellowship to help write and edit a book. In addition to advancing her career, it allowed her to work from home with her daughter.
Joining ExxonMobil
As McZeal was finishing her fellowship, she reached out to a Rice alumnus who worked at ExxonMobil, which had just gone through its merger. The company’s new optimization team would be based in Houston. This gave her an opening. She has been with ExxonMobil ever since.
She started as a research mathematician with the ExxonMobil Upstream Research Company in 2000. While she preferred linear discrete optimization, this work was nonlinear. She focused on offshore development planning: when to build platforms, how to connect them, and how to bring production economically back to shore.
“It was a large-scale MINLP optimization model for its time,” she notes, as mathematical solving and hardware accelerations have significantly evolved. “It had around 900 binaries and we thought we were geniuses because we could solve this thing.”
She has since seen optimization models get larger and more complex. Across her career, she has personally optimized (or led teams who have optimized) supply and demand, acquisition valuation, and schedules for ships carrying liquid natural gas.
Early Struggles Turn Into Strengths
McZeal started as an individual contributor but quickly became a supervisor and global functional manager. This is where her early struggles to find a major paid off.
Back at Southwestern University, her initial indecision led her to triple minor in computer science, psychology, and sociology. Computer science helped with modeling. But her psychology and sociology training equipped her with insights to be an effective leader. She enjoyed helping her teams produce their best work. And she learned to translate between the math and non-math sides of the company.
“You have to recognize that not everyone says math the way you say math,” she reflects. “It’s my job to understand what they mean, not what they say.”
That ability to understand different perspectives and communicate seamlessly with both technical and non-technical colleagues sets McZeal apart.
“Technical skills are table stakes,” she explains. “Everyone expects you to actually know your craft and to do it well... but the interpersonal skills are incredibly valuable. That's the differentiator.”
Her time choosing majors early on may have felt frustrating. But those classes ultimately helped her develop her forte.
Combining a Head for Analytics with a Heart for Service
Community service is core to McZeal’s life. She is active in her church and served on the boards of her local Girl Scouts Council, United Way Women’s Initiative, and the Greater Houston Women’s Chamber of Commerce. In addition, she is on Southwestern University’s Board of Trustees and the Advisory Board for Rice University’s School of Engineering and Computing. After receiving community support early on (advice, childcare, connections), she’s now giving it back.
In December 2025, she moved into her dream job: Community Investment Senior Advisor. She helps steward, analyze, and evaluate the impact of charitable contributions for ExxonMobil around the world.
Again, McZeal’s blend of technical and soft skills set her apart. She connects with stakeholders from Canada and Guyana to Angola and Mozambique to learn about their communities and to ensure investments are data-driven and meaningful.
Her projects include STEM education, economic development, and global health. One of her favorites is with the Clarisse Machanguana Foundation. A former WNBA player from Mozambique, Machanguana started a foundation focused on improving education, leadership, and self-esteem for young people back home, especially girls. With support from McZeal and the ExxonMobil Foundation, she runs basketball camps that also teach STEM topics.
McZeal is particularly passionate about STEM education. She explains, “We shouldn't be about making people who already have easy lives easier…But if you can figure out a way to use technology or build up a STEM workforce that can actually change their country and their world in ways that are relevant and informed by their local context, that's what makes me so excited.”
Advice for Living the Life You Want
McZeal had her first daughter as she was preparing her PhD defense and her second in her first year at ExxonMobil. “If there is an inconvenient time to have a baby, I'm all over it,” she laughs.
So how did she make it work?
“You have to know what's important to you and always keep that front and center,” she explains. For her, that was family. She stayed home when her kids were sick. When she had to choose between a meeting and a school function, she tried to choose the school function.
“That might not be the most important thing to another woman or another man. But if you align your life with what you think is most important, then decisions become a lot easier.”
She also notes that things come in seasons. Now that her daughters are grown and out of the house, she stays late if she finds a project particularly exciting.
Across her life, McZeal has had two main drivers: community and analytics. Her community supported her. Professors guided her when she did not see a path; foundations funded her PhD; friends helped with childcare.
Today, she is creating for others the kind of support that helped shape her own journey. From her church and her daughters’ schools to basketball courts in Mozambique, she brings together analytical expertise, generosity, and a deep commitment to community.
Her impact extends far beyond the problems she solves; it can be seen in the people she supports, the opportunities she creates, and the communities she leaves stronger than she found them.
